Low parallax imaging system with an internal space frame

ABSTRACT

A frame for a low parallax imaging device includes a plurality of interconnected faces configured to mount cameras. The faces are mounted along peripheral edges using kinematic connections. The frame provides a structure on which the mounted cameras provide a combined field of view of up to about 360-degrees with minimal parallax between adjacent cameras.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the National Stage of International Application No.PCT/US21/38552, filed Jun. 22, 2021, which claims benefit of priorityof: (1) U.S. Provisional Patent Application Ser. No. 63/183,961, filedMay 4, 2021, entitled “Low Parallax Imaging System with an InternalSpace Frame;” (2) International Patent Application No. PCT/US21/17284,filed Feb. 9, 2021, entitled “Panoramic Camera System for EnhancedSensing;” (3) International Application No. PCT/US20/66702, filed Dec.22, 2020, entitled “Mounting Systems for Multi-Camera Imagers;” (4)International Patent Application No. PCT/US20/39197, filed Jun. 23,2020, entitled “Opto-Mechanics of Panoramic Capture Devices withAbutting Cameras;” (5) International Patent Application No.PCT/US20/39200, filed Jun. 23, 2020, entitled “Multi-camera PanoramicImage Capture Devices with a Faceted Dome;” and (6) International PatentApplication No. PCT/US20/39201, filed Jun. 23, 2020, entitled “LensDesign for Low Parallax Panoramic Camera Systems.” The last four listedInternational applications each claims priority to U.S. ProvisionalPatent Application Ser. No. 62/952,973, filed Dec. 23, 2019, entitled“Opto-Mechanics of Panoramic Capture Devices with Abutting Cameras;” andto U.S. Provisional Patent Application Ser. No. 62/952,983, filed Dec.23, 2019, entitled “Multi-camera Panoramic Image Capture Devices with aFaceted Dome.” The last three listed International Applications aboveeach also claims priority to U.S. Provisional Patent Application Ser.No. 62/865,741, filed Jun. 24, 2019. The entirety of each of theInternational Applications and of each of the US Provisional PatentApplications listed above is hereby incorporated by reference herein.

TECHNICAL FIELD

The present disclosure relates to panoramic low-parallax multi-cameracapture devices having a plurality of adjacent and abutting polygonalcameras. The disclosure also relates the opto-mechanical design ofcameras that capture incident light from a polygonal shaped field ofview to form a polygonal shaped image, and particularly to versionsthereof using an internal space frame.

BACKGROUND

Panoramic cameras have substantial value because of their ability tosimultaneously capture wide field of view images. The earliest suchexample is the fisheye lens, which is an ultra-wide-angle lens thatproduces strong visual distortion while capturing a wide panoramic orhemispherical image. While the field of view (FOV) of a fisheye lens isusually between 100 and 180 degrees, the approach has been extended toyet larger angles, including into the 220-270° range, as provided by Y.Shimizu in U.S. Pat. No. 3,524,697. As an alternative, there are mirroror reflective based cameras that capture annular panoramic images, suchas the system suggested by P. Greguss in U.S. Pat. No. 4,930,864. Whilethese technologies have continued to evolve, it is difficult for them toprovide a full hemispheric or spherical image with the resolution andimage quality that modern applications are now seeking.

As another alternative, panoramic multi-camera devices, with a pluralityof cameras arranged around a sphere or a circumference of a sphere, arebecoming increasingly common. However, in most of these systems,including those described in U.S. Pat. Nos. 9,451,162 and 9,911,454,both to A. Van Hoff et al., of Jaunt Inc., the plurality of cameras aresparsely populating the outer surface of the device. In order to capturecomplete 360-degree panoramic images, including for the gaps or seamsbetween the adjacent individual cameras, the cameras then have widenedFOVs that overlap one to another. In some cases, as much as 50% of acamera's FOV or resolution may be used for camera to camera overlap,which also creates substantial parallax differences between the capturedimages. Parallax is the visual perception that the position or directionof an object appears to be different when viewed from differentpositions. Then in the subsequent image processing, the excess imageoverlap and parallax differences both complicate and significantly slowthe efforts to properly combine, tile or stitch, and synthesizeacceptable images from the images captured by adjacent cameras.

There are also panoramic multi-camera devices in which a plurality ofcameras is arranged around a sphere or a circumference of a sphere, suchthat adjacent cameras are abutting along a part or the whole of adjacentedges. As an example, U.S. Pat. No. 7,515,177 by K. Yoshikawa depicts animaging device with a multitude of adjacent image pickup units(cameras). Images are collected from cameras having overlapping fieldsof view, so as to compensate for mechanical errors.

More broadly, in a multi-camera device, mechanical variations in theassembly and alignment of individual cameras, and of adjacent cameras toeach other, can cause real physical variations to both the camerasthemselves, and to the seam widths and parallelism of the camera edgesalong the seams. These variations can then affect the FOVs captured bythe individual cameras, the parallax errors in the images captured byadjacent cameras, the extent of “blind spots” in the FOV correspondingto the seams, the seam widths, and the amount of image overlap that isneeded to compensate. Thus, there are opportunities to improve panoramicmulti-camera devices and the low-parallax cameras thereof, relative tothe optical and opto-mechanical designs, and other aspects as well.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 depicts a 3D view of a portion of a multi-camera capture device,and specifically two adjacent cameras thereof.

FIGS. 2A and 2B depict portions of camera lens assemblies incross-section, including lens elements and ray paths.

FIG. 3 depicts a cross-sectional view of a portion of a standardmulti-camera capture device showing FOV overlap, fields of view,overlap, seams, and blind regions.

FIG. 4 depicts two polyhedron shapes, that of a regular dodecahedron anda truncated icosahedron, to which a multi-camera capture device can bedesigned and fabricated.

FIGS. 5A and FIG. 5B depict the optical geometry for fields of view foradjacent hexagonal and pentagonal lenses, as can occur with a devicehaving the geometry of a truncated icosahedron.

FIG. 5B depicts an expanded area of FIG. 5A with greater detail.

FIG. 5C depicts an example of a low parallax (LP) volume located nearboth a paraxial NP point or entrance pupil and a device center.

FIG. 5D depicts parallax differences for two adjacent cameras, relativeto a center of perspective.

FIG. 5E depicts front color at an edge of an outer compressor lenselement.

FIG. 6 depicts distortion correction curves plotted on a graph showing apercentage of distortion relative to a fractional field.

FIG. 7 depicts fields of view for adjacent cameras, including both Coreand Extended fields of view (FOV), both of which can be useful for thedesign of an optimized panoramic multi-camera capture device.

FIG. 8 depicts an improved design for a low-parallax camera lens orobjective lens with a multi-compressor lens group.

FIG. 9 depicts an improved camera lens design, acting as an objectivelens, in combination with a refractive relay optical imaging system.

FIG. 10 depicts an electronics system diagram for a multi-camera capturedevice.

FIG. 11 depicts a concept for an internal space frame, as can be used tomount the camera channels in a multi-camera capture device.

FIG. 12A depicts concepts for a kinematic space frame.

FIGS. 12B and 12C depict side and perspective views of kinematicelements that can be used in a kinematic space frame.

FIG. 12D depicts perspective views of a kinematic element that can beused in a kinematic space frame.

FIG. 12E depicts two perspective views for partial assemblies of akinematic space frame.

FIG. 12F depicts a third perspective view for a partial assembly of akinematic space frame.

FIG. 12G depicts another perspective view of a partial assembly of akinematic space frame.

FIG. 13A, FIG. 13B, and FIG. 13C each depict an alternative kinematicspace frame structure.

FIG. 14A depicts an alternative kinematic space frame structure.

FIG. 14B and FIG. 14C depict aspects of the assembly of the FIG. 14Aspace frame.

FIG. 15A depicts both a perspective and side view of portions of acamera lens housing and features to interface it to a space frame facet.

FIG. 15B and FIG. 15C depict the assembly of camera lens housings to aspace frame.

FIG. 15D depicts a second example of the assembly of a camera channellens housing to a space frame.

DETAILED DESCRIPTION

As is generally understood in the field of optics, a lens or lensassembly typically comprises a system or device having multiple lenselements which are mounted into a lens barrel or housing, and which worktogether to produce an optical image. An imaging lens captures a portionof the light coming from an object or plurality of objects that residein object space at some distance(s) from the lens system. The imaginglens can then form an image of these objects at an output “plane”; theimage having a finite size that depends on the magnification, asdetermined by the focal length of the imaging lens and the conjugatedistances to the object(s) and image plane, relative to that focallength. The amount of image light that transits the lens, from object toimage, depends in large part on the size of the aperture stop of theimaging lens, which is typically quantified by one or more values for anumerical aperture (NA) or an f-number (F # or F/ #).

The image quality provided by the imaging lens depends on numerousproperties of the lens design, including the selection of opticalmaterials used in the design, the size, shapes (or curvatures) andthicknesses of the lens elements, the relative spacing of the lenselements one to another, the spectral bandwidth, polarization, lightload (power or flux) of the transiting light, optical diffraction orscattering, and/or lens manufacturing tolerances or errors. The imagequality is typically described or quantified in terms of lensaberrations (e.g., spherical, coma, or distortion), or the relative sizeof the resolvable spots provided by the lens, which is also oftenquantified by a modulation transfer function (MTF).

In a typical electronic or digital camera, an image sensor is nominallylocated at the image plane. This image sensor is typically a CCD or CMOSdevice, which is physically attached to a heat sink or other heatremoval means, and also includes electronics that provide power to thesensor, and read-out and communications circuitry that provide the imagedata to data storage or image processing electronics. The image sensortypically has a color filter array (CFA), such as a Bayer filter withinthe device, with the color filter pixels aligned in registration withthe image pixels to provide an array of RGB (Red, Green, Blue) pixels.Alternative filter array patterns, including the CYGM filter (cyan,yellow, green, magenta) or an RGBW filter array (W=white), can be usedinstead.

In typical use, many digital cameras are used by people or remotesystems in relative isolation, to capture images or pictures of a scene,without any dependence or interaction with any other camera devices. Insome cases, such as surveillance or security, the operation of a cameramay be directed by people or algorithms based on image content seen fromanother camera that has already captured overlapping, adjacent, orproximate image content. In another example, people capture panoramicimages of a scene with an extended or wide FOV, such as a landscapescene, by sequentially capturing a sequence of adjacent images, whilemanually or automatically moving or pivoting to frame the adjacentimages. Afterwards, image processing software, such as Photoshop orLightroom, can be used to stitch, mosaic, or tile the adjacent imagestogether to portray the larger extended scene. Image stitching or photostitching is the process of combining multiple photographic images withoverlapping fields of view to produce a segmented panorama orhigh-resolution image. Image quality improvements, including exposure orcolor corrections, can also be applied, either in real time, or in apost processing or image rendering phase, or a combination thereof.

Unless the objects in a scene are directionally illuminated and/or havea directional optical response (e.g., such as with reflectance), theavailable light is plenoptic, meaning that there is light travelling inevery direction, or nearly so, in a given space or environment. A cameracan then sample a subset of this light, as image light, with which itprovides a resulting image that shows a given view or perspective of thedifferent objects in the scene at one or more instants in time. If thecamera is moved to a different nearby location and used to captureanother image of part of that same scene, both the apparent perspectivesand relative positioning of the objects will change.

In the latter case, one object may now partially occlude another, whilea previously hidden object becomes at least partially visible. Thesedifferences in the apparent position or direction of an object are knownas parallax. In particular, parallax is a displacement or difference inthe apparent position of an object viewed along two different lines ofsight and is measured by the angle or semi-angle of inclination betweenthose two lines.

In a stereoscopic image capture or projection system, dual view parallaxis a cue, along with shadowing, occlusion, and perspective, that canprovide a sense of depth. For example, in a stereo (3D) projectionsystem, polarization or spectrally encoded image pairs can be overlapprojected onto a screen to be viewed by audience members wearingappropriate glasses. The amount of parallax can have an optimal range,outside of which, the resulting sense of depth can be too small toreally be noticed by the audience members, or too large to properly befused by the human visual system.

Whereas, in a panoramic image capture application, parallax differencescan be regarded as an error that can complicate both image stitching andappearance. In the example of an individual manually capturing apanoramic sequence of landscape images, the visual differences inperspective or parallax across images may be too small to notice if theobjects in the scene are sufficiently distant (e.g., optically atinfinity). An integrated panoramic capture device with a rotating cameraor multiple cameras has the potential to continuously capture real timeimage data at high resolution without being dependent on theuncertainties of manual capture. But such a device can also introduceits own visual disparities, image artifacts, or errors, including thoseof parallax, perspective, and exposure. Although the resulting imagescan often be successfully stitched together with image processingalgorithms, the input image errors complicate and lengthen imageprocessing time, while sometimes leaving visually obvious residualerrors.

To provide context, FIG. 1 depicts a portion of an improved integratedpanoramic multi-camera capture device 100 having two adjacent cameras120 in housings 130 which are designed for reduced parallax imagecapture. These cameras are alternately referred to as image pick-upunits, or camera channels, or objective lens systems. The cameras 120each have a plurality of lens elements (see FIG. 2 ) that are mountedwithin a lens barrel or housing 130. The adjacent outer lens elements137 have adjacent beveled edges 132 and are proximately located, onecamera channel to another, but which may not be in contact, and thus areseparated by a gap or seam 160 of finite width. Some portion of theavailable light (X), or light rays 110, from a scene or object space 105will enter a camera 120 to become image light that was captured within aconstrained FOV and directed to an image plane, while other light rayswill miss the cameras entirely. Some light rays 110 will propagate intothe camera and transit the constituent lens elements as edge-of-fieldchief rays 170, or perimeter rays, while other light rays canpotentially propagate through the lens elements to create stray or ghostlight and erroneous bright spots or images. As an example, some lightrays (167) that are incident at large angles to the outer surface of anouter lens element 137 can transit a complex path through the lenselements of a camera and create a detectable ghost image at the imageplane 150.

In greater detail, FIG. 2A depicts a cross-section of part of a camera120 having a set of lens elements 135 mounted in a housing (130, notshown) within a portion of an integrated panoramic multi-camera capturedevice 100. A fan of light rays 110 from object space 105, spanning therange from on axis to full field off axis chief rays, are incident ontothe outer lens element 137, and are refracted and transmitted inwards.This image light 115 that is refracted and transmitted through furtherinner lens elements 140, through an aperture stop 145, converges to afocused image at or near an image plane 150, where an image sensor (notshown) is typically located. The lens system 120 of FIG. 2A can also bedefined as having a lens form that consists of outer lens element 137 orcompressor lens element, and inner lens elements 140, the latter ofwhich can also be defined as consisting of a pre-stop wide angle lensgroup, and a post-stop eyepiece-like lens group. This compressor lenselement (137) directs the image light 115 sharply inwards, compressingthe light, to both help enable the overall lens assembly to provide ashort focal length, while also enabling the needed room for the cameralens housing or barrel to provide the mechanical features necessary toboth hold or mount the lens elements and to interface properly with thebarrel or housing of an adjacent camera. The image light that transiteda camera lens assembly from the outer lens element 137 to the imageplane 150 will provide an image having an image quality, that can bequantified by an image resolution, image contrast, a depth of focus, andother attributes, whose quality was defined by the optical aberrations(e.g., astigmatism, distortion, or spherical) and chromatic or spectralaberrations, encountered by the transiting light at each of the lenselements (137, 140) within a camera 120. FIG. 2B depicts a fan of chiefrays 170, or perimeter rays, incident along or near a beveled edge 132of the outer lens element 137 of the camera optics (120) depicted inFIG. 2A. FIG. 2B also depicts a portion of a captured, polygonal shapedor asymmetrical, FOV 125, that extends from the optical axis 185 to aline coincident with an edge ray.

In the camera lens design depicted in FIG. 2A, the outer lens element137 functions as a compressor lens element that redirects the transitingimage light 115 towards a second lens element 142, which is the firstlens element of the group of inner lens elements 140. In this design,this second lens element 142 has a very concave shape that isreminiscent of the outer lens element used in a fish-eye type imaginglens. This compressor lens element directs the image light 115 sharplyinwards, or bends the light rays, to both help enable the overall lensassembly to provide a short focal length, while also enabling the neededroom for the camera lens housing 130 or barrel to provide the mechanicalfeatures necessary to both hold or mount the lens elements 135 and tointerface properly with the barrel or housing of an adjacent camera.However, with a good lens and opto-mechanical design, and an appropriatesensor choice, a camera 120 can be designed with a lens assembly thatsupports an image resolution of 20-30 pixels/degree, to as much as 110pixels/degree, or greater, depending on the application and the deviceconfiguration.

The resultant image quality from these cameras will also depend on thelight that scatters at surfaces, or within the lens elements, and on thelight that is reflected or transmitted at each lens surface. The surfacetransmittance and camera lens system efficiency can be improved by theuse of anti-reflection (AR) coatings. The image quality can also dependon the outcomes of non-image light. Considering again FIG. 1 , otherportions of the available light can be predominately reflected off ofthe outer lens element 137. Yet other light that enters a camera 120 canbe blocked or absorbed by some combination of blackened areas (notshown) that are provided at or near the aperture stop, the inner lensbarrel surfaces, the lens element edges, internal baffles or lighttrapping features, a field stop, or other surfaces. Yet other light thatenters a camera can become stray light or ghost light 167 that is alsopotentially visible at the image plane.

The aggregate image quality obtained by a plurality of adjacent cameras120 within an improved integrated panoramic multi-camera capture device100 (e.g., FIG. 1 ) can also depend upon a variety of other factorsincluding the camera to camera variations in the focal length and/ortrack length, and magnification, provided by the individual cameras.These parameters can vary depending on factors including the variationsof the glass refractive indices, variations in lens element thicknessesand curvatures, and variations in lens element mounting. As an example,images that are tiled or mosaiced together from a plurality of adjacentcameras will typically need to be corrected, one to the other, tocompensate for image size variations that originate with cameramagnification differences (e.g., ±2%).

The images produced by a plurality of cameras in an integrated panoramicmulti-camera capture device 100 can also vary in other ways that effectimage quality and image mosaicing or tiling. In particular, thedirectional pointing or collection of image light through the lenselements to the image sensor of any given camera 120 can vary, such thatthe camera captures an angularly skewed or asymmetrical FOV (FOV⇄) ormis-sized FOV (FOV±). The lens pointing variations can occur duringfabrication of the camera (e.g., lens elements, sensor, and housing) orduring the combined assembly of the multiple cameras into an integratedpanoramic multi-camera capture device 100, such that the alignment ofthe individual cameras is skewed by misalignments or mounting stresses.When these camera pointing errors are combined with the presence of theseams 160 between cameras 120, images for portions of an availablelandscape or panoramic FOV that may be captured, may instead be missedor captured improperly. The variabilities of the camera pointing, andseams can be exacerbated by mechanical shifts and distortions that arecaused by internal or external environmental factors, such as heat orlight (e.g., image content), and particularly asymmetrical loadsthereof.

In comparison to the FIG. 1 system, in a typical commercially availablepanoramic camera, the seams between cameras are outright gaps that canbe 30-50 mm wide, or more. In particular, as shown in FIG. 3 , apanoramic multi-camera capture device 101 can have adjacent cameras 120or camera channels separated by large gaps or seams 160, between whichthere are blind spots or regions 165 from which neither camera cancapture images. The actual physical seams 160 between adjacent camerachannels or outer lens elements 137 (FIG. 1 and FIG. 3 ) can be measuredin various ways; as an actual physical distance between adjacent lenselements or lens housings, as an angular extent of lost FOV, or as anumber of “lost” pixels. However, the optical seam, as the distancebetween outer chief rays of one camera to another can be larger yet, dueto any gaps in light acceptance caused by vignetting or coating limits.For example, anti-reflection (AR) coatings are not typically depositedto the edges of optics, but an offsetting margin is provided, to providea coated clear aperture (CA).

To compensate for both camera misalignments and the large seams 160, andto reduce the size of the blind regions 165, the typical panoramicmulti-camera capture devices 101 (FIG. 3 ) have each of the individualcameras 120 capture image light 115 from wide FOVs 125 that provideoverlap 127, so that blind regions 165 are reduced, and the potentialcapturable image content that is lost is small. As another example, inmost of the commercially available multi-camera capture devices 101, thegaps are 25-50+ mm wide, and the compensating FOV overlap betweencameras is likewise large; e.g., the portions of the FOVs 125 that areoverlapping and are captured by two adjacent cameras 120 can be as muchas 10-50% of a camera's FOV. The presence of such large image overlapsfrom shared FOVs 125 wastes potential image resolution and increases theimage processing and image stitching time, while introducing significantimage parallax and perspective errors. These errors complicate imagestitching, as the errors must be corrected or averaged during thestitching process. In such systems, the parallax is not predictablebecause it changes as a function of object distance. If the objectdistance is known, the parallax can be predicted for given fields ofview and spacing between cameras. But because the object distance is nottypically known, parallax errors then complicate image stitching.Optical flow and common stitching algorithms determine an object depthand enable image stitching, but with processing power and time burdens.

Similarly, in a panoramic multi-camera capture device 100, of the typeof FIG. 1 , with closely integrated cameras, the width and constructionat the seams 160 can be an important factor in the operation of theentire device. However, the seams can be made smaller than in FIG. 3 ,with the effective optical seam width between the FOV edges of twoadjacent cameras determined by both optical and mechanicalcontributions. For example, by using standard optical engineeringpractices to build lens assemblies in housings, the mechanical width ofthe seams 160 between the outer lens elements 137 of adjacent camerasmight be reduced to 4-6 mm. For example, it is standard practice toassemble lens elements into a lens barrel or housing that has a minimumradial width of 1-1.5 mm, particularly near the outermost lens element.Then accounting for standard coated clear apertures or coating margins,and accounting for possible vignetting, aberrations of the entrancepupil, front color, chip edges, and trying to mount adjacent lensassemblies or housings in proximity by standard techniques. Thus, whenaccounting for both optics and mechanics, an optical seam width betweenadjacent lenses can easily be 8-12 mm or more.

But improved versions of the panoramic multi-camera capture device (300)of the type of FIG. 1 , with optical and opto-mechanical designs thatenable significantly smaller seams, and with further improved parallaxperformance, are possible. As a first example, for the presenttechnology for improved polygonal shaped cameras, during early stages offabrication of outer lens elements 137, these lenses can have a circularshape and can be AR coated to at or near their physical edges.

When these lenses are subsequently processed to add the polygonal shapedefining beveled edges 132 (e.g., FIG. 2B), a result can be that the ARcoatings will essentially extend to the beveled lens edges. Theeffective optical or coated clear apertures can then defined by anyallowances for mechanical mounting or for the standard edge grind thatis used in optics manufacturing to avoid edge chipping. With thisapproach, and a mix of other techniques that will be subsequentlydiscussed, the optical seams can be reduced to 1-5 mm width.

Aspects of the present disclosure produce high quality low-parallaxpanoramic images from an improved multi-camera panoramic capture device(300), for which portions of a first example are shown in FIG. 8 andFIG. 9 . This broad goal can be enabled by developing a systemic rangeof design strategies to inform both the optical and opto-mechanical lensdesign efforts, and the opto-mechanical device design and fabricationefforts, as well as strategies for improved image capture andprocessing. This goal can also be enabled by providing for both initialand ongoing camera and device calibration. In broad terms, the imageprocessing or rendering of images is a method to generate quality imagesfrom the raw captured image data that depends on the camera intrinsics(geometric factors such as focal length and distortion), the cameraextrinsics (geometric factors such as camera orientation to objectspace), other camera parameters such as vignetting and transmission, andillumination parameters such as color and directionality. With respectto an improved multi-camera panoramic capture device 300, the use offiducials in determining and tracking a center pixel or an imagecentroid, exposure correction, and knowledge of the camera intrinsicsfor any given camera 320 in a device, are all assists towards completingreliable and repeatable tiling of images obtained from a plurality ofadjacent cameras. Thus, the subsequent discussions are broadly focusedon providing optical (camera or objective lens) designs that can enablethe desired image quality, as well as camera and device assemblyapproaches, management of key tolerances, camera calibration, knowledgeof camera intrinsics and extrinsics, and other factors that can likewiseaffect the resultant device performance. The improved panoramicmulti-camera capture devices of the present invention can be used tosupport a wide variety of applications or markets, including cinematicimage capture, augmented reality or virtual reality (VR) image capture,surveillance or security imaging, sports or event imaging, mapping orphotogrammetry, vehicular navigation, and robotics.

Before exploring opto-mechanical means for enabling improved panoramicmulti-camera capture devices (300), means for providing cameras 120 thatare improved for use in these systems are developed. Accordingly, thegoals include providing improved cameras (320) having both reducedparallax errors and image overlap. As one aspect of the presentapproach, a goal is to reduce the residual parallax error for the edgechief rays collected respectively by each camera in an adjacent pair.The parallax error is defined as the change in parallax with respect toobject distance (e.g., that the chief ray trajectory with respect to anear distance (e.g., 3 feet) from the device, versus a far distance(e.g., 1 mile), is slightly different). For example, as one goal ortarget for reduced parallax, or to have effectively no parallax error,or to be “parallax-free”, is that the chief rays of adjacent camerasshould deviate from parallelism to each other by ≤0.5-2.0 deg., andpreferably by ≤0.01-0.1 deg. Alternately, or equivalently, the parallaxerror, as assessed as a perspective error in terms of location on theimage plane, should be reduced to ≤2 pixels, and preferably to ≤0.5pixel. As another aspect of the present approach, the width of the seams160 between adjacent cameras (e.g., 120, 320) assembled into their ownlens housings are to be reduced. The goal is to reduce the width of theseams, both in terms of their absolute physical width, and their opticalwidth or an effective width. For example, a goal is to reduce a seam 160between adjacent outer lens elements 137 to having a maximum gap or anactual physical seam width in a range of only 0.5-3.0 mm, and to thenreduce the maximum optical seam width to a range of about only 1-6 mm.As an example, these reduced seams widths can translate to a reducedangular extent of lost FOV of only 0.25-1.0°, or a number of “lost”pixels of only 2-20 pixels. For example, for a device providing 8kpixels around a 360-degree panorama equirectangular image, a loss ofonly 2-4 pixels at the seams can be acceptable as the residual imageartifacts can be difficult to perceive. The actual details or numericaltargets for effectively no-parallax error, or for the maximum opticalseam width, depend on many factors including the detailedopto-mechanical designs of the improved cameras 320 and overall device300, management of tolerances, possible allowances for a center offsetdistance or an amount of extended FOV (215) and the targets for lowparallax therein, and the overall device specifications (e.g., diameter,sensor resolution or used sensor pixels within an imaged FOV or a CoreFOV 205 (FIG. 7 )). Further goals, enabled by some combination of theabove improvements, are for each camera to reliably and quickly provideoutput images from an embedded sensor package that are cropped down toprovide core FOV images, and then that each cropped image can be readilyseamed or tiled with cropped images provided by adjacent cameras, so asto readily provide panoramic output images from an improved multi-cameracapture device (300) in real time.

In the present application for an improved multi-camera capture device(300), an improved camera 320 provided therein includes a camera lens orlens system consisting of a plurality of lens elements for providing animage, and a camera lens housing for supporting the lens elements andinterfacing with a support structure (e.g., a space frame). A camera(320) will also be equivalently referred to as a camera lens (320) or acamera channel (320).

An improved panoramic multi-camera capture device 300, such as that ofFIG. 15C, can have a plurality of camera channels 320 arranged around acircumference of a sphere to capture a 360-degree annular FOV, includingas suggested in FIG. 15C with camera channels 920 or lens housings 905.Alternately, a panoramic multi-camera capture device can have aplurality of cameras arranged around a spherical or polyhedral shape. Apolyhedron is a three-dimensional solid consisting of a collection ofpolygons that are contiguous at the edges. One polyhedral shape, asshown in FIG. 4 , is that of a dodecahedron 50, which has 12 sides orfaces, each shaped as a regular pentagon 55, and 20 vertices or corners(e.g., a vertex 60). A panoramic multi-camera capture device formed tothe dodecahedron shape has cameras with a pentagonally shaped outer lenselements that nominally image a 69.1° full width field of view. Anothershape is that of a truncated icosahedron, like a soccer ball, which asis also shown in FIG. 4 , and has a combination of 12 regular pentagonalsides or faces, 20 regular hexagonal sides or faces, 60 vertices, and 90edges. More complex shapes, with many more sides, such as regularpolyhedra, Goldberg polyhedra, or shapes with octagonal sides, or evensome irregular polyhedral shapes, can also be useful. For example, aGoldberg chamfered dodecahedron is similar to the truncated icosahedron,with both pentagonal and hexagonal facets, totaling 42 sides. But ingeneral, the preferred polyhedrons for the current purpose have sides orfaces that are hexagonal or pentagonal, which are generally roundishshapes with beveled edges 132 meeting at obtuse corners. Otherpolyhedral shapes, such as an octahedron or a regular icosahedron can beused, although they have triangular facets. Polyhedral facets with moreabrupt or acute corners, such as square or triangular faces, can beeasier to fabricate, as compared to facets with pentagonal and orhexagonal facets, as they have fewer edges to cut to provide polygonaledges on the outermost lens element, so as to define a capturedpolygonal FOV. However, greater care can then be needed in cutting,beveling, and handling the optic because of those acute corners.Additionally, for lens facets with large FOVs and acute facet angles, itcan be more difficult to design the camera lenses and camera lenshousings for optical and opto-mechanical performance. Typically, a 360°polyhedral camera will not capture a full spherical FOV as at least partof one facet is sacrificed to allow for support features and power andcommunications cabling, such as via a mounting post. However, if thedevice communicates wirelessly, and is also hung by a thin cable to avertex, the FOV lost to such physical connections can be reduced.

As depicted in FIG. 1 and FIG. 2B, a camera channel 120 can resembles afrustum, or a portion thereof, where a frustum is a geometric solid(normally a cone or pyramid) that lies between one or two parallelplanes that cut through it. In that context, a fan of chief rays 170corresponding to a polygonal edge, can be refracted by an outercompressor lens element 137 to nominally match the frustum edges inpolyhedral geometries.

To help illustrate some issues relating to camera geometry, FIG. 5Aillustrates a cross-sections of a pentagonal lens 175 capturing apentagonal FOV 177 and a hexagonal lens 180 capturing a hexagonal FOV182, representing a pair of adjacent cameras whose outer lens elementshave pentagonal and hexagonal shapes, as can occur with a truncatedicosahedron, or soccer ball type panoramic multi-camera capture devices(e.g., 100, 300). The theoretical hexagonal FOV 182 spans a half FOV of20.9°, or a full FOV of 41.8° (θ₁) along the sides, although the FOVnear the vertices is larger. The pentagonal FOV 177 supports 36.55° FOV(θ₂) within a circular region, and larger FOVs near the corners orvertices. Notably, in this cross-section, the pentagonal FOV 177 isasymmetrical, supporting a 20-degree FOV on one side of an optical axis185, and only a 16.5-degree FOV on the other side of the optical axis.

Optical lenses are typically designed using programs such as ZEMAX orCode V. Design success typically depends, in part, on selecting the bestor most appropriate lens parameters, identified as operands, to use inthe merit function. This is also true when designing a lens system foran improved low-parallax multi-camera panoramic capture device (300),for which there are several factors that affect performance (including,particularly parallax) and several parameters that can be individuallyor collectively optimized, so as to control it. One approach targetsoptimization of the “NP” point, or more significantly, variants thereof.

As background, in the field of optics, there is a concept of theentrance pupil, which is a projected image of the aperture stop as seenfrom object space, or a virtual aperture which the imaged light raysfrom object space appear to propagate towards before any refraction bythe first lens element. By standard practice, the location of theentrance pupil can be found by identifying a paraxial chief ray fromobject space 105, that transits through the center of the aperture stop,and projecting or extending its object space direction forward to thelocation where it hits the optical axis 185. In optics, incident Gaussor paraxial rays are understood to reside within an angular range ≤10°from the optical axis, and correspond to rays that are directed towardsthe center of the aperture stop, and which also define the entrancepupil position. Depending on the lens properties, the entrance pupil maybe bigger or smaller than the aperture stop, and located in front of, orbehind, the aperture stop.

By comparison, in the field of low-parallax cameras, there is a conceptof a no-parallax (NP) point, or viewpoint center. Conceptually, the “NPPoint” has been associated with a high FOV chief ray or principal rayincident at or near the outer edge of the outermost lens element, andprojecting or extending its object space direction forward to thelocation where it hits the optical axis 185. For example, depending onthe design, camera channels in a panoramic multi-camera capture devicecan support half FOVs with non-paraxial chief rays at angles >31° for adodecahedron type system (FIG. 4 ) or >20° for a truncated icosahedrontype system (see FIG. 4 and FIG. 5A). This concept of the NP pointprojection has been applied to the design of panoramic multi-cameracapture devices, relative to the expectations for chief ray propagationand parallax control for adjacent optical systems (cameras). It is alsostated that if a camera is pivoted about the NP point, or a plurality ofcamera's appear to rotate about a common NP point, then parallax errorswill be reduced, and images can be aligned with little or no parallaxerror or perspective differences. But in the field of low parallaxcameras, the NP point has also been equated to the entrance pupil, andthe axial location of the entrance pupil that is estimated using a firstorder optics tangent relationship between a projection of a paraxialfield angle and the incident ray height at the first lens element (seeFIGS. 2A, 2B).

Thus, confusingly, in the field of designing of low-parallax cameras,the NP point has also been previously associated with both with theprojection of edge of FOV chief rays and the projection of chief raysthat are within the Gauss or paraxial regime. As will be seen, inactuality, they both have value. In particular, an NP point associatedwith the paraxial entrance pupil can be helpful in developing initialspecifications for designing the lens, and for describing the lens. AnNP point associated with non-paraxial edge of field chief rays can beuseful in targeting and understanding parallax performance and indefining the conical volume or frustum that the lens assembly can residein.

The projection of these non-paraxial chief rays can miss the paraxialchief ray defined entrance pupil because of both lens aberrations andpractical geometry related factors associated with these lens systems.Relative to the former, in a well-designed lens, image quality at animage plane is typically prioritized by limiting the impact ofaberrations on resolution, telecentricity, and other attributes. Withina lens system, aberrations at interim surfaces, including the aperturestop, can vary widely, as the emphasis is on the net sums at the imageplane. Aberrations at the aperture stop are often somewhat controlled toavoid vignetting, but a non-paraxial chief ray need not transit thecenter of the aperture stop or the projected paraxially located entrancepupil.

To expand on these concepts, and to enable the design of improved lowparallax lens systems, it is noted that the camera lens system 120 inFIG. 2A depicts both a first NP point 190A, corresponding to theentrance pupil as defined by a vectoral projection of paraxial chiefrays from object space 105, and an offset second NP point 190B,corresponding to a vectoral projection of a non-paraxial chief rays fromobject space. Both of these ray projections cross the optical axis 185in locations behind both the lens system and the image plane 150. Aswill be subsequently discussed, the ray behavior in the region betweenand proximate to the projected points 190A and 190B can be complicatedand neither projected location or point has a definitive value or size.A projection of a chief ray will cross the optical axis at a point, buta projection of a group of chief rays will converge towards the opticalaxis and cross at different locations, that can be tightly clustered(e.g., within a few or tens of microns), where the extent or size ofthat “point” can depends on the collection of proximate chief rays usedin the analysis. Whereas, when designing low parallax imaging lensesthat image large FOVs, the axial distance or difference between the NPpoints 190A and 190B that are provided by the projected paraxial andnon-paraxial chief rays can be significantly larger (e.g., millimeters).Thus, as will also be discussed, the axial difference represents avaluable measure of the parallax optimization (e.g., a low parallaxvolume 188) of a lens system designed for the current panoramic capturedevices and applications. As will also be seen, the design of animproved device (300) can be optimized to position the geometric centerof the device, or device center 196, outside, but proximate to this lowparallax volume 188, or alternately within it, and preferably proximateto a non-paraxial chief ray NP point.

As one aspect, FIG. 5A depicts the projection of the theoretical edge ofthe fields of view (FOV edges 155), past the outer lens elements (lenses175 and 180) of two adjacent cameras, to provide lines directed to acommon point (190). These lines represent theoretical limits of thecomplex “conical” opto-mechanical lens assemblies, which typically arepentagonally conical or hexagonally conical limiting volumes. Again,ideally, in a no-parallax multi-camera system, the entrance pupils or NPpoints of two adjacent cameras are co-located. But to avoid mechanicalconflicts, the mechanics of a given lens assembly, including the sensorpackage, should generally not protrude outside a frustum of a camerasystem and into the conical space of an adjacent lens assembly. However,real lens assemblies in a multi-camera panoramic capture device are alsoseparated by seams 160. Thus, the real chief rays 170 that are acceptedat the lens edges, which are inside of both the mechanical seams and aphysical width or clear aperture of a mounted outer lens element (lenses175 and 180), when projected generally towards a paraxial NP point 190,can land instead at offset NP points 192, and be separated by an NPpoint offset distance 194.

This can be better understood by considering the expanded area A-A inproximity to a nominal or ideal point NP 190, as shown in detail in FIG.5B. Within a hexagonal FOV 182, light rays that propagate within theGauss or paraxial region (e.g., paraxial ray 173), and that pass throughthe nominal center of the aperture stop, can be projected to a nominalNP point 190 (corresponding to the entrance pupil), or to an offset NPpoint 190A at a small NP point difference or offset 193 from a nominalNP point 190. Whereas, the real hexagonal lens edge chief rays 170associated with a maximum inscribed circle within a hexagon, can projectto land at a common offset NP point 192A that can be at a larger offsetdistance (194A). The two adjacent cameras in FIGS. 5A,B also may or maynot share coincident NP points (e.g., 190). Distance offsets can occurdue to various reasons, including geometrical concerns between cameras(adjacent hexagonal and pentagonal cameras), geometrical asymmetrieswithin a camera (e.g., for a pentagonal camera), or from limitationsfrom the practical widths of seams 160, or because of the directionalitydifference amongst aberrated rays.

As just noted, there are also potential geometric differences in theprojection of incident chief rays towards a simplistic nominal “NPpoint” (190). First, incident imaging light paths from near the cornersor vertices or mid-edges (mid-chords) of the hexagonal or pentagonallenses may or may not project to common NP points within the describedrange between the nominal paraxial NP point 190 and an offset NP point192B. Also, as shown in FIG. 5B, just from the geometric asymmetry ofthe pentagonal lenses, the associated pair of edge chief rays 170 and171 for the real accepted FOV, can project to different nominal NPpoints 192B that can be separated from both a paraxial NP point (190) byan offset distance 194B and from each other by an offset distance 194C.

As another issue, during lens design, the best performance typicallyoccurs on axis, or near on axis (e.g., ≤0.3 field (normalized)), nearthe optical axis 185. In many lenses, good imaging performance, bydesign, often occurs at or near the field edges, where optimizationweighting is often used to force compliance. The worst imagingperformance can then occur at intermediate fields (e.g., 0.7-0.8 of anormalized image field height). Considering again FIG. 5A,B,intermediate off axis rays, from intermediate fields (θ) outside theparaxial region, but not as extreme as the edge chief rays(10°<θ<20.9°), can project towards intermediate NP points between anominal NP point 190 and an offset NP point 192B. But other, moreextreme off axis rays, particularly from the 0.7-0.8 intermediatefields, that are more affected by aberrations, can project to NP pointsat locations that are more or less offset from the nominal NP point 190than are the edge of field offset NP points 192B. Accounting for thevariations in lens design, the non-paraxial offset “NP” points can falleither before (closer to the lens) the paraxial NP point (the entrancepupil) as suggested in FIG. 5B, or after it (as shown in FIG. 2A).

This is shown in greater detail in FIG. 5C, which essentiallyillustrates a further zoomed-in region A-A of FIG. 5B, but whichillustrates an impact from vectoral projected ray paths associated withaberrated image rays, that converge at and near the paraxial entrancepupil (190), for an imaging lens system that was designed and optimizedusing the methods of the present approach. In FIG. 5C, the projected raypaths of green aberrated image rays at multiple fields from a cameralens system converge within a low parallax volume 188 near one or more“NP” points. Similar illustrations of ray fans can also be generated forRed or Blue light. The projection of paraxial rays 173 can converge ator near a nominal paraxial NP point 190, or entrance pupil, located on anominal optical axis 185 at a distance Z behind the image plane 150. Theprojection of edge of field rays 172, including chief rays 171, convergeat or near an offset NP point 192B along the optical axis 185. The NPpoint 192B can be quantitatively defined, for example, as the center ofmass of all edge of field rays 172. An alternate offset NP point 192Acan be identified, that corresponds to a “circle of least confusion”,where the paraxial, edge, and intermediate or mid-field rays, aggregateto the smallest spot. These different “NP” points are separated from theparaxial NP point by offset distances 194A and 194B, and from each otherby an offset distance 194C. Thus, it can be understood that an aggregate“NP point” for any given real imaging lens assembly or camera lens thatsupports a larger than paraxial FOV, or an asymmetrical FOV, istypically not a point, but instead can be an offset low parallax (LP)smudge or volume 188.

Within a smudge or low parallax volume 188, a variety of possibleoptimal or preferred NP points can be identified. For example, an offsetNP point corresponding to the edge of field rays 172 can be emphasized,so as to help provide improved image tiling. An alternate mid-field(e.g., 0.6-0.8) NP point (not shown) can also be tracked and optimizedfor. Also the size and position of the overall “LP” smudge or volume188, or a preferred NP point (e.g., 192B) therein, can change dependingon the lens design optimization. Such parameters can also vary amongstlenses, for one fabricated lens system of a given design to another, dueto manufacturing differences amongst lens assemblies. Although FIG. 5Cdepicts these alternate offset “NP points” 192A,B for non-paraxial raysas being located after the paraxial NP point 190, or further away fromthe lens and image plane, other lenses of this type, optimized using themethods of the present approach, can be provided where similarnon-paraxial NP points 192A,B that are located with a low parallaxvolume 188 can occur at positions between the image plane and theparaxial NP point.

FIG. 5C also shows a location for a center of the low-parallaxmulti-camera panoramic capture device, device center 196. Based onoptical considerations, an improved panoramic multi-camera capturedevice 300 can be preferably optimized to nominally position the devicecenter 196 within the low parallax volume 188. Optimized locationstherein can include being located at or proximate either of the offsetNP points 192A or 192B, or within the offset distance 194B between them,so as to prioritize parallax control for the edge of field chief rays.The actual position therein depends on parallax optimization, which canbe determined by the lens optimization relative to spherical aberrationof the entrance pupil, or direct chief ray constraints, or distortion,or a combination thereof. For example, whether the spherical aberrationis optimized to be over corrected or under corrected, and how weightingson the field operands in the merit function are used, can affect thepositioning of non-paraxial “NP” points for peripheral fields or midfields. The “NP” point positioning can also depend on the management offabrication tolerances and the residual variations in lens systemfabrication. The device center 196 can also be located proximate to, butoffset from the low parallax volume 188, by a center offset distance198. This approach can also help tolerance management and provide morespace near the device center 196 for cables, circuitry, coolinghardware, and the associated structures. In such case, the adjacentcameras 120 can then have offset low parallax volumes 188 of “NP” points(FIG. 5D), instead of coincident ones (FIGS. 5A, B). In this example, ifthe device center 196 is instead located at or proximate to the paraxialentrance pupil, NP point 190, then effectively one or more of the outerlens elements 137 of the cameras 120 are undersized and the desired fullFOVs are not achievable.

Thus, while the no-parallax (NP) point is a useful concept to worktowards, and which can valuably inform panoramic image capture andsystems design, and aid the design of low-parallax error lenses, it isidealized, and its limitations must also be understood. Considering thisdiscussion of the NP point(s) and LP smudges, in enabling an improvedlow-parallax multi-camera panoramic capture device (e.g., lens design320 of FIG. 8 ), it is important to understand ray behavior in thisregime, and to define appropriate parameters or operands to optimize,and appropriate target levels of performance to aim for. In the lattercase, for example, a low parallax lens with a track length of 65-70 mmcan be designed for in which the LP smudge is as much as 10 mm wide(e.g., offset distance 194A). But alternate lens designs, for which thisparameter is further improved, can have a low parallax volume 188 with alongitudinal LP smudge width or width along the optical axis (offset194A) of a few millimeters or less.

The width and location of the low parallax volume 188, and the vectoraldirections of the projections of the various chief rays, and their NPpoint locations within a low parallax volume, can be controlled duringlens optimization by a method using operands associated with a fan ofchief rays 170 (e.g., FIGS. 2A,B). But the LP smudge or LP volume 188 ofFIG. 5C can also be understood as being a visualization of thetransverse component of spherical aberration of the entrance pupil, andthis parameter can be used in an alternate, but equivalent, designoptimization method to using chief ray fans. In particular, during lensoptimization, using Code V for example, the lens designer can create aspecial user defined function or operand for the transverse component(e.g., ray height) of spherical aberration of the entrance pupil, whichcan then be used in a variety of ways. For example, an operand value canbe calculated as a residual sum of squares (RSS) of values across thewhole FOV or across a localized field, using either uniform ornon-uniform weightings on the field operands. In the latter case oflocalized field preferences, the values can be calculated for a locationat or near the entrance pupil, or elsewhere within a low parallax volume188, depending on the preference towards paraxial, mid, or peripheralfields. An equivalent operand can be a width of a circle of leastconfusion in a plane, such as the plane of offset NP point 192A or thatof offset NP 192B, as shown in FIG. 5C. The optimization operand canalso be calculated with a weighting to reduce or limit parallax errornon-uniformly across fields, with a disproportionate weighting favoringperipheral or edge fields over mid-fields. Alternately, the optimizationoperand can be calculated with a weighting to provide a nominally lowparallax error in a nominally uniform manner across all fields (e.g.,within or across a Core FOV 205, as in FIG. 7 ). That type ofoptimization may be particularly useful for mapping applications.

The concept of parallax correction, with respect to centers ofperspective, is illustrated in FIG. 5D. A first camera lens 120Acollects and images light from object space 105 into at least a CoreFOV, including light from two outer ray fans 179A and 179B, whose chiefray projections converge towards a low parallax volume 188A. These rayfans can correspond to a group of near edge or edge of field rays 172,as seen in FIG. 2B or FIG. 5C. As was shown in FIG. 5C, within an LPvolume 188, the vectoral projection of such rays from object space,generally towards image space, can cross the optical axis 185 beyond theimage plane, at or near an alternate NP point 192B that can be selectedor preferred because it favors edge of field rays. However, as is alsoshown in FIG. 5C, such edge of field rays 172 need not cross the opticalaxis 185 at exactly the same point. Those differences, when translatedback to object space 105, translate into small differences in theparallax or perspective for imaged ray bundles or fans within or acrossan imaged FOV (e.g., a Core FOV 205, as in FIG. 7 ) of a camera lens.

A second, adjacent camera lens 120B, shown in FIG. 5D, can provide asimilar performance, and image a fan of chief rays 170, including rayfan 179C, from within a Core FOV 205 with a vectoral projection of thesechief rays converging within a corresponding low parallax volume 188B.LP volumes 188A and 188B can overlap or be coincident, or be offset,depending on factors including the camera geometries and the seamsbetween adjacent cameras, or lens system fabrication tolerances andcompensators, or on whether the device center 196 is offset from the LPvolumes 188. The more overlapped or coincident these LP volumes 188 are,the more overlapped are the centers of perspective of the two lenssystems. Ray Fan 179B of camera lens 120A and ray fan 179C of cameralens 120B are also nominally parallel to each other; e.g., there is noparallax error between them. However, even if the lens designs allowvery little residual parallax errors at the FOV edges, fabricationvariations between lens systems can increase the differences.

Analytically, the chief ray data from a real lens can also be expressedin terms of perspective error, including chromatic errors, as a functionof field angle. Perspective error can then be analyzed as a positionerror at the image between two objects located at different distances ordirections. Perspective errors can depend on the choice of COP location,the angle within the imaged FOV, and chromatic errors. For example, itcan be useful to prioritize a COP so as to minimize green perspectiveerrors. Perspective differences or parallax errors can be reduced byoptimizing a chromatic axial position (Δz) or width within an LP volume188 related to a center of perspective for one or more field angleswithin an imaged FOV. The center of perspective can also be graphed andanalyzed as a family of curves, per color, of the Z (axial) interceptposition (distance in mm) versus field angle. Alternately, to get abetter idea of what a captured image will look like, the COP can begraphed and analyzed as a family of curves for a camera system, as aparallax error in image pixels, per color, versus field.

During the design or a camera lens systems, a goal can be to limit theparallax error to a few pixels or less for imaging within a Core FOV 205(FIG. 7 ). Alternately, it can be preferable to particularly limitparallax errors in the peripheral fields, e.g., for the outer edges of aCore FOV and for an Extended FOV region (if provided). If the residualparallax errors for a camera are thus sufficiently small, then theparallax differences seen as a perspective error between two adjacentcameras near their shared seam 160, or within a seam related region ofextended FOV overlap imaging, can likewise be limited to several pixelsor less (e.g., ≤3-4 pixels). Depending on the lens design, devicedesign, and application, it can be possible and preferable to reduceparallax errors for a lens system further, as measured by perspectiveerror, to ≤0.5 pixel for an entire Core FOV, the peripheral fields, orboth. If these residual parallax errors for each of two adjacent camerasare small enough, images can be acquired, cropped, and readily tiled,while compensating for or hiding image artifacts from any residual seams160 or blind regions 165.

In pursuing the design of a panoramic camera of the type of that of FIG.1 , but to enable an improved low-parallax multi-camera panoramiccapture device (300), having multiple adjacent cameras, the choices oflens optimization methods and parameters can be important. A camera lens120, or system of lens elements 135, like that of FIG. 2A, can be usedas a starting point. The camera lens has compressor lens element(s), andinner lens elements 140, the latter of which can also be defined asconsisting of a pre-stop wide angle lens group, and a post-stopeyepiece-like lens group. In designing such lenses to reduce parallaxerrors, it can be valuable to consider how a fan of paraxial tonon-paraxial chief rays 125 (see FIG. 2A), or a fan of edge chief rays170 (see FIG. 2B), or localized collections of edge of field rays 172(see FIG. 5C) or 179 A,B (see FIG. 5D) are imaged by a camera lensassembly. It is possible to optimize the lens design by using a set ofmerit function operands for a collection or set (e.g., 31 defined rays)of chief rays, but the optimization process can then become cumbersome.As an alternative, in pursuing the design of an improved low-parallaxmulti-camera panoramic capture device (300), it was determined thatimproved performance can also be obtained by using a reduced set of rayparameters or operands that emphasizes the transverse component ofspherical aberration at the entrance pupil, or at a similar selectedsurface or location (e.g., at an offset NP point 192A or 192B) within anLP smudge volume 188 behind the lens system. Optimization for atransverse component of spherical aberration at an alternatenon-paraxial entrance pupil can be accomplished by using merit functionweightings that emphasize the non-paraxial chief rays.

As another aspect, in a low-parallax multi-camera panoramic capturedevice, the fans of chief rays 170 that are incident at or near abeveled edge of an outer lens element of a camera 120 (see FIG. 2B)should be parallel to a fan of chief rays 170 that are incident at ornear an edge 132 of a beveled surface of the outer lens element of anadjacent camera (see FIG. 1 ). It is noted that an “edge” of an outerlens element 137 or compressor lens is a 3-dimensional structure (seeFIG. 2B), that can have a flat edge cut through a glass thickness, andwhich is subject to fabrication tolerances of that lens element, theentire lens assembly, and housing 130, and the adjacent seam 160 and itsstructures. The positional definition of where the beveled edges are cutinto the outer lens element depends on factors including the materialproperties, front color, distortion, parallax correction, tolerances,and an extent of any extra extended FOV 215. An outer lens element 137becomes a faceted outer lens element when beveled edges 132 are cut intothe lens, creating a set of polygonal shaped edges that nominally followa polygonal pattern (e.g., pentagonal or hexagonal).

A camera system 120 having an outer lens element with a polygonal shapethat captures incident light from a polygonal shaped field of view canthen form a polygonal shaped image at the image plane 150, wherein theshape of the captured polygonal field of view nominally matches theshape of the polygonal outer lens element. The cut of these bevelededges for a given pair of adjacent cameras can affect both imaging andthe optomechanical construction at or near the intervening seam 160.

As another aspect, FIG. 5E depicts “front color”, which is a differencein the nominal ray paths by color versus field, as directed to an offaxis or edge field point. Typically, for a given field point, the bluelight rays are the furthest offset. As shown in FIG. 5E, the acceptedblue ray 157 on a first lens element 137 is AX mm further out than theaccepted red ray 158 directed to the same image field point. If the lenselement 137 is not large enough, then this blue light can be clipped orvignetted and a color shading artifact can occur at or near the edges ofthe imaged field. Front color can appear in captured image content as anarrow rainbow-like outline of the polygonal FOV or the polygonal edgeof an outer compressor lens element 437 which acts as a field stop forthe optical system. Localized color transmission differences that cancause front color related color shading artifacts near the image edgescan be caused by differential vignetting at the beveled edges of theouter compressor lens element 137, or from edge truncation at compressorlens elements 438 (FIG. 13A), or through the aperture stop 145. Duringlens design optimization to provide an improved camera lens (320), frontcolor can be reduced (e.g., to ΔX≤0.5 mm width) as part of the chromaticcorrection of the lens design, including by glass selection within thecompressor lens group or the entire lens design, or as a trade-off inthe correction of lateral color. The effect of front color on capturedimages can also be reduced optomechanically, by designing an improvedcamera lens (320) to have an extended FOV 215 (FIG. 7 ), and also theopto-mechanics to push straight cut or beveled lens edges 132 at orbeyond the edge of the extended FOV 215, so that any residual frontcolor occurs outside the core FOV 220. The front color artifact can thenbe eliminated during an image cropping step during image processing. Theimpact of front color or lateral color can also be reduced by aspatially variant color correction during image processing. As anotheroption, an improved camera lens (320) can have a color dependentaperture at or near the aperture stop, that can, for example, provide alarger transmission aperture (diameter) for blue light than for red orgreen light.

Optical performance at or near the seams can be understood, in part,relative to distortion (FIG. 6 ) and a set of defined fields of view(FIG. 7 ). In particular, FIG. 7 depicts potential sets of fields ofview for which potential image light can be collected by two adjacentcameras. As an example, a camera with a pentagonally shaped outer lenselement, whether associated with a dodecahedron or truncated icosahedronor other polygonal lens camera assembly, with a seam 160 separating itfrom an adjacent lens or camera channel, can image an ideal FOV 200 thatextends out to the vertices (60) or to the polygonal edges of thefrustum or conical volume that the lens resides in. However, because ofthe various physical limitations that can occur at the seams, includingthe finite thicknesses of the lens housings, the physical aspects of thebeveled lens element edges, mechanical wedge, and tolerances, a smallercore FOV 205 of transiting image light can actually be imaged. Thecoated clear aperture for the outer lens elements 137 should encompassat least the core FOV 205 with some margin (e.g., 0.5-1.0 mm). As thelens can be fabricated with AR coatings before beveling, the coatingscan extend out to the seams. The core FOV 205 can be defined as thelargest low parallax field of view that a given real camera 120 canimage. Equivalently, the core FOV 205 can be defined as the sub-FOV of acamera channel whose boundaries are nominally parallel to the boundariesof its polygonal cone (see FIGS. 5A and 5B). Ideally, with small seams160, and proper control and calibration of FOV pointing, the nominalCore FOV 205 approaches or matches the ideal FOV 200 in size.

During a camera alignment and calibration process, a series of imagefiducials 210 can be established along one or more of the edges of acore FOV 205 to aid with image processing and image tiling or mosaicing.The resulting gap between a core FOV 205 supported by a first camera andthat supported by an adjacent camera can result in blind regions 165(FIG. 5A, B). To compensate for the blind regions 165, and theassociated loss of image content from a scene, the cameras can bedesigned to support an extended FOV 215, which can provide enough extraFOV to account for the seam width and tolerances, or an offset devicecenter 196. As shown in FIG. 7 , the extended FOV 215 can extend farenough to provide overlap 127 with an edge of the core FOV 205 of anadjacent camera, although the extended FOVs 215 can be larger yet. Thislimited image overlap can result in a modest amount of image resolutionloss, parallax errors, and some complications in image processing aswere previously discussed with respect to FIG. 3 , but it can also helpreduce the apparent width of seams and blind regions. However, if theextra overlap FOV is modest (e.g., ≤5%) and the residual parallax errorstherein are small enough (e.g. ≤0.75 pixel perspective error), asprovided by the present approach, then the image processing burden canbe very modest. Image capture out to an extended FOV 215 can also beused to enable an interim capture step that supports camera calibrationand image corrections during the operation of an improved panoramicmulti-camera capture device 300. FIG. 7 also shows an inscribed circlewithin one of the FOV sets, corresponding to a subset of the core FOV205, that is the common core FOV 220 that can be captured in alldirections from that camera. The angular width of the common core FOV220 can be useful as a quick reference for the image capacity of acamera. An alternate definition of the common core FOV 220 that islarger, to include the entire core FOV 205, can also be useful. Thedashed line (225) extending from the common core FOV 220 or core FOV205, to beyond the ideal FOV 200, to nominally include the extended FOV215, represents a region in which the lens design can support carefulmapping of the chief or principal rays or control of sphericalaberration of the entrance pupil, so as to enable low-parallax errorimaging and easy tiling of images captured by adjacent cameras.

Across a seam 160 spanning the distance between two adjacent usableclear apertures between two adjacent cameras, to reduce parallax andimprove image tiling, it can be advantageous if the image light iscaptured with substantial straightness, parallelism, and common spacingover a finite distance. The amount of FOV overlap needed to provide anextended FOV and limit blind regions can be determined by controllingthe relative proximity of the entrance pupil (paraxial NP point) or analternate preferred plane within a low parallax volume 188 (e.g., toemphasize peripheral rays) to the device center 196 (e.g., to the centerof a dodecahedral shape). The amount of Extended FOV 215 is preferably5% or less (e.g., ≤1.8° additional field for a nominal Core FOV of37.5°), such that a camera's peripheral fields are then, for example,˜0.85-1.05). If spacing constraints at the device center, andfabrication tolerances, are well managed, the extended FOV 215 can bereduced to ≤1% additional field. Within an extended FOV 215, parallaxshould be limited to the nominal system levels, while both imageresolution and relative illumination remain satisfactory. The parallaxoptimization to reduce parallax errors can use either chief ray or pupilaberration constraints, and targeting optimization for a high FOV region(e.g., 0.85-1.0 field), or beyond that to include the extra cameraoverlap regions provided by an extended FOV 215 (e.g., FIG. 7 , afractional field range of ˜0.85-1.05).

In addition, in enabling an improved low-parallax multi-camera panoramiccapture device (300), with limited parallax error and improved imagetiling, it can be valuable to control image distortion for image lighttransiting at or near the edges of the FOV, e.g., the peripheral fields,of the outer lens element. In geometrical optics, distortion is adeviation from a preferred condition (e.g., rectilinear projection) thatstraight lines in a scene remain straight in an image. It is a form ofoptical aberration, which describes how the light rays from a scene aremapped to the image plane. In general, in lens assemblies used for imagecapture, for human viewing it is advantageous to limit image distortionto a maximum of +/−2%. In the current application, for tiling orcombining panoramic images from images captured by adjacent cameras,having a modest distortion of ≤2% can also be useful. As a reference, inbarrel distortion, the image magnification decreases with distance fromthe optical axis, and the apparent effect is that of an image which hasbeen mapped around a sphere (or barrel). Fisheye lenses, which are oftenused to take hemispherical or panoramic views, typically have this typeof distortion, as a way to map an infinitely wide object plane into afinite image area. Fisheye lens distortion (251) can be large (e.g., 15%at full field or 90° half width (HW)), as a deviation from f-thetadistortion, although it is only a few percent for small fields (e.g.,≤30° HW). As another example, in laser printing or scanning systems,f-theta imaging lenses are often used to print images with minimalbanding artifacts and image processing corrections for pixel placement.In particular, F-theta lenses are designed with a barrel distortion thatyields a nearly constant spot or pixel size, and a pixel positioningthat is linear with field angle θ, (h=f*θ).

Thus, improved low-parallax cameras 320 that capture half FOVs of≤35-40° might have fisheye distortion 251, as the distortion may be lowenough. However, distortion can be optimized more advantageously for thedesign of improved camera lens assemblies for use in improvedlow-parallax multi-camera panoramic capture devices (300). As a firstexample, as shown in FIG. 6 , it can be advantageous to provide cameralens assemblies with a localized nominal f-theta distortion 250A at ornear the edge of the imaged field. In an example, the image distortion250 peaks at ˜0.75 field at about 1%, and the lens design is notoptimized to provide f-theta distortion 250 below ˜0.85 field. However,during the lens design process, a merit function can be constrained toprovide a nominally f-theta like distortion 250A or an approximatelyflat distortion 250B, for the imaged rays at or near the edge of thefield, such as for peripheral fields spanning a fractional field rangeof ˜0.9-1.0. This range of high fields with f-theta type or flatteneddistortion correction includes the fans of chief rays 170 or perimeterrays of FIG. 2B, including rays imaged through the corners or vertices60, such as those of a lens assembly with a hexagonal or pentagonalouter lens element 137. Additionally, because of manufacturingtolerances and dynamic influences (e.g., temperature changes) that canapply to a camera 120, including both lens elements 135 and a housing130, and to a collection of cameras 120 in a panoramic multi-cameracapture device, it can be advantageous to extend the region of nominalf-theta or flattened distortion correction in peripheral fields tobeyond the nominal full field (e.g., 0.85-1.05). This is shown in FIG.6, where a region of reduced or flattened distortion extends beyond fullfield to ˜1.05 field. In such a peripheral field range, it can beadvantageous to limit the total distortion variation to ≤0.5% or less.Controlling peripheral field distortion keeps the image “edges” straightin the adjacent pentagonal shaped regions. This can allow more efficientuse of pixels when tiling images, and thus faster image processing.

The prior discussion treats distortion in a classical sense, as an imageaberration at an image plane. However, in low-parallax cameras, thisresidual distortion is typically a tradeoff or nominal cancelation ofcontributions from the compressor lens elements (137, or 437 and 438 inFIG. 13A) versus those of the aggregate inner lens elements (140, or 440in FIG. 13A). Importantly, the ray re-direction caused by the distortioncontribution of the outer compressor lens element also affects both theimaged ray paths and the projected chief ray paths towards the lowparallax volume. This in turn means that for the design of at least somelow-parallax lenses, distortion optimization can affect parallax or edgeof field NP point or center of perspective optimization.

The definitions of the peripheral fields or a fractional field range 225of (e.g., ˜0.85-1.05, or including ≤5% extra field), in which parallax,distortion, relative illumination, resolution, and other performancefactors can be carefully optimized to aid image tiling, can depend onthe device and camera geometries. As an example, for hexagonal shapedlenses and fields, the lower end of the peripheral fields can be definedas ˜0.83, and for pentagonal lenses, ˜0.8. Although FIG. 7 wasillustrated for a case with two adjacent pentagon-shaped outer lenselements and FOV sets, the approach of defining peripheral fields andExtended FOVs to support a small region of overlapped image capture, canbe applied to multi-camera capture device designs with adjacentpentagonal and hexagonal cameras, or to adjacent hexagonal cameras, orto cameras with other polygonal shapes or with adjacent edges of anyshape or contour generally.

For an Extended FOV 215 to be functionally useful, the nominal imageformed onto an image sensor that corresponds to a core FOV 205 needs tounderfill the used image area of the image sensor, by at least enough toallow an extended FOV 215 to also be imaged. This can be done to helpaccount for real variations in fabricated lens assemblies from theideal, or for the design having an offset device center 196, as well asfabrication variations in assembling an improved low-parallaxmulti-camera panoramic capture device (300). But as is subsequentlydiscussed, prudent mechanical design of the lens assemblies can impactboth the imaged field of view of a given camera and the seams betweenthe cameras, to limit mechanical displacements or wedge and help reduceparallax errors and FOV overlap or underlap. Likewise, tuning the imageFOV (core FOV 205) size and position with compensators or with fiducialsand image centroid tracking and shape tracking can help. Taken togetherin some combination, optimization of distortion and low or zero parallaximaging over extended peripheral fields, careful mechanical design tolimit and compensate for component and assembly variations, and the useof corrective fiducials or compensators, can provide a superior overallsystems solution. As a result, a captured image from a camera canreadily be cropped down to the nominal size and shape expected for thenominal core FOV 205, and images from multiple cameras can then bemosaiced or tiled together to form a panoramic image, with reducedburdens on image post-processing. However, an extended FOV 215, ifneeded, should provide enough extra angular width (e.g., θ₁≤5% of theFOV) to match or exceed the expected wedge or tilt angle q₂, that canoccur in the seams, θ₁≥θ₂.

In designing an improved imaging lens of the type that can be used in alow-parallax panoramic multi-camera capture device (100 or 300), severalfirst order parameters can be calculated so as to inform the designeffort. A key parameter is the target size of the frustum or conicalvolume, based on the chosen polygonal configuration (lens size (FOV) andlens shape (e.g., pentagonal)) and the sensor package size. Other keyparameters that can be estimated include the nominal location of theparaxial entrance pupil, the focal lengths of the compressor lens groupand the wide-angle lens group, and the FOV seen by the wide-angle group.

But the design optimization for an improved camera lens (320) for use inan improved low-parallax panoramic multi-camera capture devices (300)also depends on how the numerous other lens attributes and performancemetrics are prioritized. In particular, the relevant system parameterscan include the control of parallax or the center of perspective (COP)error at the edges of an imaged field or for inner field locations orboth, as optimized using fans of chief rays or spherical aberration ofthe entrance pupil). These parameters are closely linked with other keyparameters including the width and positions of the “LP smudge” orvolume 188, the size of any center offset distance between the entrancepupil or LP smudge and the device center 196, the target width of thegaps or seams, the extent of blind regions 165, and the size of anymarginal or extended FOV to provide overlap. The relevant performancemetrics can include image resolution or MTF, distortion (particularly inthe peripheral fields, and distortion of the first compressor lenselement and of the compressor lens group), lateral color, relativeillumination, front color, and color vignetting, telecentricity, andghosting. Other relevant design variables can include mechanical andmaterials parameters such as the number of compressor lens elements, theconfiguration of the compressor lens group, the wide-angle lens groupand eyepiece lens group, glass choices, the allowed maximum size of thefirst compressor or outer lens element, the sensor package size, thetrack length, the nominal distance from the image plane to the nearestprior lens element (e.g., working distance), the nominal distance fromthe image plane to the entrance pupil, the nominal distance from theimage plane or the entrance pupil to the polygonal center or devicecenter, manufacturing tolerances and limits, and the use ofcompensators. As a second illustrative example, FIG. 8 depicts a lensdesign for an alternate improved camera lens 320 or objective lens withlens elements 335, that is an enhanced version of the lens 120 of FIG.2A that can be used in an improved low-parallax multi-camera panoramiccapture device (300). FIG. 8 illustrates the overall lens form on theleft, and a zoomed in portion that illustrates the inner lens elements350 in greater detail, but FIG. 8 does not include an illustration of alens housing to support these lens elements. This lens system, which isalso designed for a dodecahedral system, has lens elements 335 thatincludes both a first lens element group or compressor lens groupconsisting of outer lens element 345 a and compressor lens elements 345b and 345 c, and inner lens elements 350. In this design, compressorelements 345 b,c are not quite combined as a cemented or air spacedoublet. As also shown in FIG. 8 , inner lens elements 350 consists of afront wide-angle lens group 365 and a rear eyepiece like lens group 367.

In FIG. 8 , the lens system of camera 320 collects light rays 310 fromobject space 305 to provide image light 315 from a field of view 325,and directs them through lens elements 335, which consist of outer lenselements 340 and inner lens elements 350, to provide an image at animage plane 360. This lens system provides improved image quality,telecentricity, and parallax control, although these improvements arenot obvious in FIG. 8 . In this example, the outer lens elements 340comprise a group of three compressor lens elements 345 a, 345 b, and 345c, and the optical power, or light bending burden, is shared amongst themultiple outer lens elements. Image light 310 from object space 305 isrefracted and transmitted through a first lens element group orcompressor lens group 340 having three lens elements, such that chiefrays at 37.377 deg. at the vertices are redirected at a steep angle of˜80 deg. towards the optical axis 385.

This compressor lens element group is followed by a second lens elementgroup or wide-angle lens element group 365, which consists of the twolens elements between the compressor lens element group and the aperturestop 355. A third lens element group or eyepiece lens group 367, whichhas five lens elements, redirects the transiting image light coming fromthe aperture stop 355 to provide image light telecentrically at F/2.8 toan image sensor at an image plane 360. As this lens is designed for adodecahedral system, the first lens element 345 a nominally acceptsimage light for a FOV width of 31.717 deg. at the mid-chords. The chiefray projections converge or point towards an LP smudge 392 whichincludes a paraxially defined entrance pupil.

Although this type of camera lens, or lens form, as exemplified by FIG.8 , with a first lens element group or compressor lens group or lenselement (345 a,b,c), a pre-stop second lens element group or wide anglelens group 365, and a post-stop third lens element group oreyepiece-like lens group 367, may in entirety, or in part, visuallyresemble a fisheye lens, it is quite different. Unlike the present lensdesign (e.g., FIG. 8A), a fisheye lens is an ultra-wide-angle lens thathas heavily overcorrected spherical aberration of the pupil such thatits entrance pupil is positioned near the front of the lens, inproximity to the first lens element. This pupil aberration also causessubstantial shifts and rotations for the non-paraxial entrance pupilsrelative to the paraxial one. Such a lens is also reverse telephoto toprovide a long back focal length, and a positive value for a ratio ofthe entrance pupil to image plane distance (EPID), divided by the lensfocal length (EPID/EFL). A fisheye lens also provides a strong visualdistortion that typically follows a monotonic curve (e.g., H=fθ(f-theta)), that images with a characteristic convex non-rectilinearappearance. The typical fisheye lens captures a nominal 180° wide fullFOV, although fisheye lenses that capture images with even larger FOVs(270-310°) have been described in literature. By comparison, theimproved low-parallax wide-angle camera lenses 320 of the presentapproach, used in an improved low-parallax multi-camera panoramiccapture device (300), are purposefully designed with low distortion,particularly at or near the edges of the imaged FOV, so as to ease imagecropping and tiling. Also, the present cameras, while wide angle,typically capture image light from a significantly smaller FOV than dofisheye lenses. For example, a camera for a regular dodecahedral devicenominally captures images from a full width FOV of ≈63-75°. Whereas, anoctahedral device can have cameras nominally capturing image light froma full width FOV of 71-110° width, a truncated icosahedral device canhave cameras nominally capturing image light from a full width FOV of≈40-45° width.

While the internal combination of the pre-stop wide angle lens group 365and the post-stop eyepiece lens group 367, are not used as a stand-alonesystem for the present applications, if the compressor lens group 345a,b,c was removed, these two inner groups can also work together to formimages at or near the image plane or sensor. In the optical designs ofthe camera lenses (320), these lens groups, and particularly thewide-angle lens group 365, visually resembles a door peeper lens design.However, while this combination of two groups of lens elements again mayvisually appear similar to a fisheye or door-peeper type lens, theyagain do not image with fisheye type f-theta lens distortion (e.g.,H=fθ).

By comparison, the optical construction of the rear lens group (367), orsub-system, resembles that of an eyepiece, similar to those used asmicroscopic or telescopic eyepieces, but used in reverse, and without aneye being present. Eyepieces are optical systems where the entrancepupil is invariably located outside of the system. The entrance pupil ofthe eyepiece, where an eye would be located in a visual application,nominally overlaps with the plane where the aperture stop 355 islocated. Likewise, the nominal input image plane in a visual applicationcorresponds to the sensor plane (950) in the present application. Theeyepiece lens group (367) was not designed to work with an eye, and thusdoes not satisfy the requirements for an actual eyepiece relative to eyerelief, accommodation, FOV, and pupil size. But this eyepiece-like lensgroup solves a similar problem, and thus has a similar form to that ofan eyepiece. Depending on the application, the optical design can moreor less provide nominal optical performance similar to that of a moretypical eyepiece.

This improved lens 320 of FIG. 8 , is similar to the camera lens 120 ofFIGS. 2A,B, but it has been designed for a more demanding set ofconditions relative to parallax correction, a larger image size (4.3 mmwide), and a further removed entrance pupil to provide more room for useof a larger sensor board. This type of configuration, with multiplecompressor lens elements, can be useful for color correction, as theglass types can be varied to advantageously use both crown and flinttype glasses. In this example, the outer lens element 345 a, or firstcompressor lens is a meniscus shaped lens element of SLAH52 glass, withan outer surface 338 with a radius of curvature of ˜55.8 mm, and aninner surface with a radius of curvature of ˜74.6 mm. Thus, an overalloptimized improved multi-camera capture device 500 can have a nominalradius from the vertex of the outer lens element to a nominal NP pointlocation of ˜65 mm. In this example, incident light 310 from objectspace 305 that becomes image light 315 is significantly refractedinwards (towards the optical axis 385) when it encounters the outersurface 338, but it is refracted inwards less dramatically than isprovided by the first surface of the FIG. 2A lens.

The requirement to use a larger sensor board increases the distancebetween the image sensor plane and the entrance pupil or low parallaxvolume 392. In particular, the focal length is larger (5.64 mm) so as toproject the image onto a large sensor. Within the LP smudge or lowparallax volume 392, there are several potentially useful planes orlocations of reference, including the paraxial entrance pupil, or alocation of a center of perspective, or locations for non-paraxial chiefray NP points, or a location of a circle of least confusion where the LPsmudge or parallax volume has a minimal size in the plane tangent to theoptical axis. The entrance pupil is a good reference as it is readilycalculated from a common first order optics equation. The axial locationof a center of perspective is also a good reference as it is directlyrelatable to perceived image quality. While the distance from the imageplane 360 to any of these locations can be used as a reference, anoffset distance 375 to a paraxial entrance pupil can be preferred. Inthis example (FIG. 8 ), the entrance pupil is located ˜30 mm behind theimage plane 360, for a negative entrance pupil distance to focal lengthratio, EPID/EFL=−5.3:1. Depending on how it is measured, the LP smudge392 can have an axial width of ≤2 mm.

The improved camera lens systems 320 of FIG. 8 provides an example forhow the lens form can vary from that depicted in FIGS. 2A,B. In general,the lens form for enabling an improved low-parallax multi-camerapanoramic capture device (300) has a common feature set, consisting ofan initial compressor lens group which bends the light sharply towardsthe optical axis, a physically much smaller wide angle lens group whichredirects the light into the aperture stop, and an eyepiece-like lensgroup which directs and focuses the transiting image light to an imageplane. The requirement to reduce parallax or perspective errors, whileenabling multiple polygonal shaped cameras to be adjacently abutted toform a larger improved low-parallax multi-camera panoramic capturedevice (300) brings about an extreme lens form, where lens elements inthe compressor lens group can be rather large (e.g., 80-120 mm indiameter), while typically at least some lens elements in the wide-angleand eyepiece lens groups are simultaneously rather small (e.g., 5-10 mmin diameter). In these type of lens designs, the first compressor lenselement or outermost lens element 345 a, and adjacent outer lenselements of adjacent lens systems, can alternately be part of acontiguous faceted dome or shell. It is also typical that several (e.g.,2-4) of the lens element surfaces have aspheric or conic surfaceprofiles, so as to bend or direct light rays transiting near the edgesof the lens elements differently than those transiting near the centeror optical axis. Typically, the wide-angle lens group 365 also has alens element with a deeply concave surface. In some cases, duringoptimization, that surface can want to become hyper-hemispherical,although to improve element manufacturability, such profiles arepreferably avoided. Another measure of the extreme characteristics ofthis lens form, is the offset distance of the paraxial entrance pupil(or similarly, the LP smudge) behind or beyond the image plane. Unliketypical lenses, the entrance pupil is not in front of the image planebut is instead pushed far behind or beyond it. This is highlighted bythe negative entrance pupil to image plane distance/focal length ratio,EPID/EFL, which can range from −2:1 to −10:1, but which is typically≥−4:1 in value.

Optimization of the size, position, and characteristics of the LP smudgeor low parallax volume 392, as depicted in exemplary detail in FIG. 8 ,impacts the performance and design of the improved camera lens systems320. The low parallax volume optimization is heavily impacted by themerit function parameters and weightings on chief rays for bothspherical aberration of the entrance pupil and axial or longitudinalchromatic aberration of the entrance pupil. Lens element and lens barrelfabrication tolerances can also impact the size and positioning of thisvolume, or equivalently, the amount of residual parallax error, providedby the lens. Thus, even though these lenses can be considered to have anextreme form, optimization can help desensitize the designs tofabrication errors, and provide insights on how and where to providecorrective adjustments or compensators.

Enhanced situational awareness can be directly enabled by an improvedlow-parallax multi-camera panoramic capture device (300) with a lowparallax camera lens 300, such as that of FIG. 8 , with an appropriatelens design and use of optical detectors or sensors. For example, anoptical event detection sensor, such the Oculi SPU, can be positioned atthe image plane 360, and use its fast response and large dynamic rangeto detect abrupt changes of an object in a scene. The neuromorphic orevent sensor technology is still relatively early in its development,and at present these sensors tend to have low spatial resolutioncompared to CCD or CMOS image sensors. Thus, as an alternative forproviding situational awareness, a high resolution, large pixel countimage sensor, such as the Teledyne Emerald 67M, with an addressable 67mega-pixels, can be located at the image plane 360 of an appropriatelydesigned lens 320. However, as this sensor is large, and a camerachannel 320 needs to fit within a conical volume or frustum, the frontcompressor lens elements (345 a,b,c) can become very large and bedifficult to fabricate. These issues can be addressed by a reducing thesensor size (such as to a Teledyne Emerald 16M or 36M), or by reducingthe FOV imaged by the camera lens, or a combination thereof. Forexample, if the overall polygonal form is changed from a dodecahedron toa regular truncated icosahedron, the imaged field of view captured by acamera lens (32) is decreased, a larger sensor can be supported, and thelens image quality improved, resulting in an improved angularresolution.

As another approach that can enable higher resolution imaging or dualmodality sensing, and various situational awareness possibilities, animproved low-parallax multi-camera panoramic capture device (300) caninclude a low parallax camera lens 320, acting as an objective lens,paired with an imaging relay optical system. FIG. 9 depicts such asystem, with objective or camera lens 320, including a compressor lensgroup 340, paired with an imaging relay 400, where the relay is a lenssystem having a nominal magnification of 1.5×. These lenses arenominally aligned along an optical axis 385. In FIG. 9 , the examplecamera lens 320 is similar to the one of FIG. 8 , although the frontcompressor lens group 340 includes a cemented doublet. In this type ofsystem, the original image plane 360 corresponds to a real aerial imagethat is an intermediate image to a second image plane 410 at the far endof the imaging relay. A large high resolution image sensor, such as theTeledyne 67M, can then be provided at this second image plane 410. Theoptical system would be appropriately designed so that the opticalresolution and the sensor resolution approximately match. The aperturestop 355 of the objective lens (320) is nominally re-imaged to asecondary aperture stop 455 with the relay optics. The optical relaydesign 400 also includes a gap or clearance 420 between the outersurface of the last field lens element 430 and subsequent lens elements.The relay optical system can also include one or more beamsplitters todirect light to a secondary optical sensor, such as an IR imaging sensoror an event sensor, that is provided at an offset or secondary imageplane. The optical system of FIG. 9 can be assembled around and througha nexus type internal frame (e.g., FIG. 11 ) that provides a hollowcenter or open space through which multiple imaging beams of image lightfrom multiple camera channels can cross through each other.

FIG. 10 then depicts an example electronics system diagram for amulti-camera capture device 300 of the type of FIG. 1 , where the camerachannels 120 are arranged in a dodecahedral geometry and directly imageto the respective sensors. Image data can be collected from each of the11 cameras 320, and directed through an interface input-output module,through a cable or bundle of cables, to a portable computer that canprovide image processing, including live image cropping and stitching ortiling, as well as camera and device control. The output image data canbe directed to an image display, a VR headset, or to further computers,located locally or remotely. Electrical power and cooling can also beprovided as needed. To help reduce thermal gradients between the sensorsand their electronics, and the optics, micro-heat pipes or Peltierdevices can be used to cool the sensors and re-direct the heat. The heatmay be removed from the overall device by either active or passivecooling provided through the electro-mechanical interface in the twelfthcamera position, shown in FIG. 10 . This cooling can be provided byconvection or conduction (including liquid cooling) or a combinationthereof. Outside ambient or environmental factors can also affectperformance of a multi-camera capture device 300. This approach can alsobe used with multi-camera capture devices 300 having other geometries,including ones have camera channels that include imaging relays (FIG. 9).

FIG. 11 depicts an example mechanical configuration for an internalspace frame that can be used in an improved multi-camera capture device300. In particular, FIG. 11 illustrates a mounting assembly comprising anexus internal frame 500, with numerous pentagonal faces 510 arranged ina regular dodecahedral pattern with a hollow center. Generally, theinternal frame 500 is a polygonal-shaped frame that has an array ofadjacent mechanical faces have peripheral edges that form a polygonalshape and have mounting and alignment features. The internal frame 500can be designed as a mount or mechanical assembly to support an11-camera system, with a support post attaching in the 12th position(similar to FIG. 10 ). A polygonal internal frame, or half or partialinternal frame can also be used in a partial or hemispheric system,where the camera assemblies, including imaging sensors are mounteddirectly or indirectly to the frame. Connections, cables, and wiring fordata transfer and cooling can then be directed out through the openpolygonal portion 530 of a face 510 and into the hollow center of theinternal frame 500 and out through an open polygonal portion 530 ofanother face 510. Alternately, a hemispherical system with an internalmounting frame 500 can provide a central hollow or open space (e.g., anexus) to enable image light beams to cross through an opposing pair ofopen polygonal portion 530 of faces 510 so as to transit subsequentrelay optical systems (400) and reach remote optical sensors at asecondary image plane 410. Positionally, the width of the gap orclearance 420 in the relay optics (see FIG. 9 ) between the outersurface of the last field lens element 430 and the nearest subsequentlens elements 435 nominally matches the width of the central hollowvolume between opposing faces 510 provided by the nexus internal frame500. For example, clearance 420 can be 75 mm wide. But it is noted thatthe objective lens housings or the relay lens field lens elements 430and their housing can protrude modestly through the open polygonalportion 530 of face 510, and into the central volume of the hollowcenter 540, as long as they do not block imaging light of an adjacentobjective lens 320. In such a case, the clearance between lens elementswould be less than the width of the hollow center of the internal frame800. For example, width of clearance 420 can be several millimeterssmaller than the central width of the hollow center 540.

As shown in FIG. 11 , a nexus internal frame 500 can have a pentagonalface (510A) that can have three adjustors 520, such as set screws orflexures, oriented nominally 120° apart, that can interact with mountingand alignment features on the camera housing and thus be used to helpalign a given camera channel. For an improved multi-camera panoramicimage capture device 300 constructed in a dodecahedral pattern, theinternal frame would also be dodecahedral with pentagonal faces and itwould be oriented with the internal pentagonal faces nominally alignedwith the external pentagonal geometry. The internal space frame approachcan be used with other polygonal device structures, such as that for anoctahedron, an icosahedron, or a chamfered dodecahedron. In such cases,at least some of the space frame faces include edges along theirperiphery that correspond to other polygonal shapes, such as hexagonal.

An internal frame 500 can be machined separately and assembled from 2 ormore pieces that are mounted together, or it can be made as a singlepiece structure by casting or 3D printing. Although the fabrication of asingle piece frame could be more complex, the resulting structure can bemore rigid and robust, and may support tighter mechanical tolerances.For example, a dodecahedral frame (500) with a hollow center could becast in stainless steel, and then selectively post-casting machined onthe faces 510 to provide precision datum features, including flats,vee-slots, or ball mounting features. In particular, one or morepentagonal faces 510A, 510B, or 510C can be provided with one or moreadjustors 520 that can be used to nudge the respective camera channelagainst a precision v-groove structure (not shown in FIG. 11 ). Thesev-groove structures can be fabricated into, or protruding from, aninside edge of a pentagonal vertex 60 of a pentagonal face. Alignmentballs can be mounted to the faces 510 or to the interfacing adjacentlens housings, or to a combination thereof. A variety of features,including balls, vees, flats, and sockets can be used to enablekinematic constraints between the lens housings or between the lenshousings and the space frame 500. This internal frame 500 can then beprovided with flexures or adjustors on all or most of the pentagonalfaces, to provide kinematic type adjustments and to reduce or avoid overconstraint during device assembly and use.

As previously, the mounting and adjustments for secondary channels canhave a different design or configuration than those for a primarychannel. In these improved devices (300), springs, flexures, magnets, oradhesives can be used on or within an internal frame 500 to provide alow stress mechanical linkage or connection between the lens housings ofadjacent camera channels, and also between the camera channels and thenexus internal frame 500, or between different portions of the internalframe, so at help limit under-constraint or over-constraint between theassemblies or lens housings. As another option, an internal frame can beat least in part made with a more compliant material, such as brass orInvar. A 3D printed frame can be fabricated from materials includingplastic, bronze, or steel.

An internal space frame for an improved multi-camera capture device 300can also be a kinematic structure, in which individual faces (510) areattached to each other using kinematic features. While the resultingspace frame structure can be less rigid, it can be easier and lesscostly to fabricate and assemble the individual faces than to machine orcast an entire or unitary space frame. However, in that case, theassembled space frame should be a kinematic structure, so that it canrespond and compensate or correct for external loads. Kinematicinterfaces between the space frame faces can also help the kinematicinteractions between the adjacent camera channels that are attached tothe space frame. An exactly constrained or kinematic structure (theseterms can be used interchangeably) will also largely avoid stress anddeformation when assembled in the face of manufacturing variation. Itwill also exhibit precision, returning to a consistent position as itexperiences uniform temperature changes. These properties make it idealfor optical supporting structures. The number of kinematic componentscan be based on the requirements of the system.

FIG. 12A depicts an example of a dodecahedral exactly constrained spaceframe structure or kinematic space frame 600 with each pentagonal face610 (or facet or side) being an independent exactly constrained element.Each face 610 has nominally straight edges along the periphery to form apolygonal shape, which in this example, is pentagonal. In otherexamples, the edges may be other than straight, and/or there may be moreor fewer edges. FIG. 12A is illustrated to show key features that enablethe kinematics of the space frame 600. Each pentagonal face 610 includesten mounting points 690, e.g., two per polygonal edge 680. A constrainedface 610 is provided with a particular set of kinematic elements 650 ata subset of its ten common mounting points 690, where the type ofkinematic element 650 used depends on the location of the face 610 andthe associated mounting point 690 within the overall structure (spaceframe 600). In FIG. 12A, some of the faces 610 are depicted withkinematic elements 650 at the mounting points 690, and some without, sothat the mounting points can be seen. These mounting points 690 aredepicted as rectangular cut outs. The locations of the mounting points690 along an edge 680 can be anywhere, but the positioning the mountingpoints 690 close to the vertices 60 may improve structural stability. Akinematic element 650 straddles a seam 615 between adjacent mountingpoints 690 of two adjacent faces 610 to provide a kinematic interface orconnection. The combination of kinematic elements 650 arrayed about thespace frame 600 will act to prevent or reduce over-constraint within theassembly. FIG. 12A depicts an example kinematic space frame structurewith faces 610 that include an open polygonal center 630 or openingthrough which a camera channel lens housing (not shown) can be mountedor inserted. However additional example features on the pentagonal faces610 for mounting or aligning a lens housing of a camera channel are notshown.

The kinematic elements 650, mounted at points 690, can properly orientthemselves at angles between the faces 610 so as to remove differentnumbers of degrees of freedom (DOF). Embodiments of these types ofkinematic elements 650 are shown. In FIG. 12B, a kinematic element 650A,e.g., as an example of the kinematic element 650, that can be used toremove a single degree of freedom is depicted in both a perspective viewand a side view. This kinematic element 650A is embodied as a sphere onplane. It includes two components, a ball mount 652 with a ball 655 orpartial ball, and a flat mount 657 with a flat 660. Features 662 forproviding a holding force or constraint vector 664 are only partiallyshown in this figure. Balls or partial balls for use in this type ofkinematic element can be obtained from Bal-tec (Los Angeles, Calif.).

In FIG. 12C, a second kinematic element 650B, e.g., as an example of thekinematic element 650, that can be used to remove two degrees of freedomis depicted in both a perspective view and a side view. In this example,the kinematic element 650B is embodied as a sphere in a vee socket, andit includes two components, a ball mount 652 with a single ball 655 orsingle partial ball, and a vee mount 666 with a vee 668. In this figure,both components, the ball and flat mounts, include a hole 662. Amechanism such as a spring (not shown) can provide a holding force thatprovides along constraint vectors 664.

In FIG. 12D, a third kinematic element 650C is depicted in perspectiveview, showing two adjoining components that can be used to remove threedegrees of freedom. In this example, the kinematic element 650C isembodied as a sphere in a trihedral socket, and it includes twocomponents, a ball mount 652 with a single ball 655 or partial ball, anda socket mount 670 with a socket 672. Again, example hole features (662)are provided for attaching a holding force mechanism. This kinematicelement can operate like a spherical joint or Heim joint.

In a kinematic space frame 600, substitution of these kinematic elements650 can be employed consisting of alternative elements such ascombinations of wire, blade or notch flexures or ball and socket jointsand act only to remove the indicated degrees of freedom between attachedelements. The sum of the constraint vectors 664 will nominally alignwith the bisecting angle between adjacent faces 610. For the examplekinematic elements 650 that are shown, it is assumed that nesting orholding forces can be applied to keep the surfaces in contact andprevent under-constraint. These forces, represented by constraintvectors 664 can be accomplished via force elements such as holdingsprings (not shown) that are mounted at holes 662. Alternately, or inaddition, holding forces can be provided by magnets, elastics,adhesives, gravity, or by active externally applied forces such as frompiezo-electric devices, solenoids, or air or electromotive cylinders(pneumatics), or combinations thereof.

There are several different ways to create the constraint patternnecessary for an exactly constrained structure using these elements.Although any face 610 of the space frame 600 can be considered fixed,for this explanatory discussion, it will be assumed that the top surfaceis fixed to ground (e.g., to a stable mounting surface duringfabrication). On the left, FIG. 12E shows a partial space frame 600 witha top face 611 and one of the adjacent faces 610 pointing downward at anappropriate angle for a dodecahedral shaped structure. Two kinematicelements 650 are shown connecting the faces 610 across a seam 615. Inthis example, the kinematic element 650 on the left is of the type of650C that removes three degrees of freedom (DOF), and the kinematicelement on the right is of the type of 650B that removes two DOF. Thepattern of constraints produced will allow a single degree of freedom ofrotation around the line (shown as a dashed line) connecting the centersof the two spheres. On the right, FIG. 12E depicts a more completepartial space frame 600 with an additional adjacent face 610 providedwith the same constraints pattern attaching it to the upper face 611 orground, having a left-to-right pair of connecting kinematic elements650C and 650B as were provided with the prior face. The two constraintshere will remove two rotational degrees of freedom (one for each face610, the top face 611 is fixed to ground). A kinematic element 650B ofthe ball and vee type (FIG. 12C) to remove two DOFs is provided in thelower seam 615 to connect the left and right faces 610 together. Theresult is a rigid structure. The rest of a hemisphere portion of thisexample dodecahedral space frame 500 is then built upon thissub-structure.

FIG. 12F depicts a further assembly of the partial kinematic space frame600, including a next face 610 added to this the hemispheric portion. Asthe three previously added faces 610 described in FIG. 12E result in arigid structure, the remaining faces 610 in the hemispheric portion maybe constrained differently. An added face 610, on the lower right isconstrained to the grounded upper face 611 via two elements of the typeof 650B with the orientation of the vees (668) aligned in the directionof the intersection of the two faces 610 and 611. This will allowrotation around the dashed line shown as well as translation along thatline. Again, a kinematic element 650B of the ball and vee type (FIG.12C) to remove 2 DOFs is provided in the lower seam 615 to connect theright face 610 to the pair of faces to the left. This kinematic elementin the style of 650B between the prior rigid structure and this new facewill remove an additional 2 degrees of freedom and result in anadditional rigid element. Faces 610 can be added around the top face 611in a similar manner to complete a hemisphere portion of the partialkinematic space frame 600.

Alternately, a similar rigid structure for a partial kinematic spaceframe 600 can be achieved by having the two initial faces (single degreeof freedom faces) at the end of the chain of faces 610 as well as thebeginning. Also, the single degree of freedom faces can straddle thefaces with 4 degrees of freedom with the same rigid kinematic structureresulting. FIG. 12G then shows two hemispheres or partial kinematicspace frames combined into a single dodecahedral kinematic space frame600. The two hemispheres are connected via a connection that is in thespirit of a “Maxwell” or 2-2-2 type kinematic connection. In principle,a 2-2-2 connection consists of three spheres or balls in three veeslargely at 120 degree spacing. A portion of a 2-2-2 connection 675 isshown in FIG. 12G, where space frame 600 has two single degree offreedom kinematic elements 650A (e.g., FIG. 12B) on either side of avertex, connecting the upper and lower hemispheric portions of the spaceframe together. These two nearly adjacent single degree of freedomkinematic elements 650A effectively act as a dual degree of freedomkinematic element 650B. Note that the connection in this case isgenerated by a simple rotation of the planar element 90 degrees aboutthe line that is largely through the center of the sphere that lies inthe plane that is perpendicular to both faces 610 and in the plane ofthe face with the planar element attachment. The two other kinematicconnections, being the two degrees of freedom v-groove type kinematicelements 650B are on the opposite side of the space frame and are notshown as they are not visible. Those two kinematic elements 650B in thestyle of FIG. 12C, can be mounted near the upper to lower hemispherevertices 60 of two adjacent faces 610. The orientation of the kinematicelements three are symmetric to a large extent to minimize decentrationwith thermal movement. Alternatively, these two kinematic elements 650Bcan be mounted at two mounting points (690) of a single face 610,potentially sacrificing some kinematic purity for increased robustness.

The size, assembly considerations, and/or requirements of the system maydrive modifications or adaptations in the constraint pattern. FIG. 13Ashows an alternative example dodecahedral kinematic space frame 700 witha crown-like “solid” upper hemispheric portion 720 with an arrangementof six fixed continuous faces 730 with solid joints or continuous seams745. The crown 715 may be machined from a bulk material, created via anadditive manufacturing processing, or the like. The lower hemisphericportion consists of discretized faces 710 connected with the kinematicelements 650, such as the kinematic elements 650A,B,C presentedpreviously. The crown structure 715 in the upper hemispheric portion 720can be useful in interfacing with other system mechanics that requiregreater robustness or rigidity. Lens housings can be mounted on both thefixed faces 730 and the kinematic faces 710.

However, the crown structure 715 is more likely used as to mechanicallyinterface to other devices or structures, including a lattice work (notshown) that can support image relay systems (FIG. 9 ). As analternative, the crown structure 715 can have a cylindrical base and aset of outward flared extensions that come to points at the vertices.This could be an alternate upper structure in FIG. 13A, while the lowerhemisphere still comprises discretized faces 710 with kinematic elements650.

As another alternative kinematic space frame 700, FIG. 13B shows ahemisphere upper portion 720 that includes a “fixed” section 725 havingtwo adjacent solid or continuous polygonal faces 740 that have a solidjoint or continuous seam 745. For instance, the second 725 may bemachined from a bulk material. In this example, the upper hemisphere isbroken into three identical sections 725, each with two faces 740. Onefixed section 725 includes the top face, and the other fixed sectionsare connected to it using a 2-2-2 type connection using an array ofkinematic elements 650 of the type (650B of FIG. 12C). Thus, two fixedsections 725 are connected to each other with 3 spheres in 3 vees.Again, the lower hemispheric portion consists of discretized faces 710that are interconnected with the kinematic elements 650, such as thekinematic elements 650A,B,C presented previously.

FIG. 13C depicts a third alternative example, where the space frame 700consists of two hemispheric crown portions 715A and 715B that aremachined, cast, or printed to each have a set of continuous faces 740.Kinematic mounting using an appropriate set of kinematic elements 650locate the two crown halves to each other to provide a complete spaceframe 700. When the two crown halves are apart, access to the fastenersthat hold the camera lens housings to the space frame is comparativelyeasy. The two crown halves can be held together with fasteners that areaccessed through an opening at the bottom. Each crown 715 can be asingle piece cast part, with selective external machining. In general,the inside surfaces of the crowns do not need precise features. However,for improved camera devices 300 with crown-like space frame portions(e.g., FIG. 13A and 13C) that require high precision alignmenttolerances, a 5 or 6 axis milling machine may be needed to fabricatethese structures.

For the example alternate space frames of FIG. 13A, FIG. 13B, and FIG.13C, the upper and lower hemispheric portions of the space frames 700are connected to each other using an appropriate arrangement ofkinematic elements 650 (e.g., kinematic elements 650A or 650B). Thesealternative space frames 700 can be useful in reducing the number ofconstituent individual parts and in improving robustness of the overallspace frame. Also, other combinations are possible. For example, a crownstructure 715 as depicted in the upper hemisphere 720 of FIG. 13A can becombined with the approach depicted in the upper hemisphere of FIG. 13Bthat uses an intermediate number of continuous faces 725. These types ofspace frames with partial combinations of discrete and solid faceskinematically connected can be extended to other multi-face polygonalshapes, such as the truncated icosahedron (soccer ball) or the chamfereddodecahedron.

FIG. 14A depicts another alternative example kinematic space frame 800to that of FIG. 12A and FIGS. 13A, 13B, 13C, again having a dodecahedralgeometry with 12 faces or facets. Faces 810 can include channel vees 815to which camera channel lens housings (not shown) can be mounted. FIG.14B depicts an example assembly process for a plate or face 810 that canbe used in the FIG. 14A space frame. A series of retention pins 820 areadded to the face 810, by mounting them into drilled holes with springs825 secured within the face 810 to the available end of the pins 820.Thereafter, a rolling pin like cylindrical pin 830 is added, and ispulled by springs 825 against a pair of machined v-grooves 835 that areprovided on edges 840. Each spring spans a distance from a retention pin820 to a narrow end of a rolling-pin like cylindrical pin 830. To resistbending under load, these cylindrical pins 830 can be made of steel.

This same assembly process can then be repeated for all 12-space framefaces 810 and their accompanying pins, springs, and cylinders, althoughnot all edges 840 of all faces 810 will be initially equipped withcylindrical pins 830. Then as depicted in FIG. 14C, the individual faces810 are connected to form a space frame 800 of the type of FIG. 14A. Oneface 811, and corresponding lens channel, which is opposite the mountingplate or face 812, can be identified as a primary channel. The secondaryfaces 810 are connected to the primary face using the springs, withsprings on a polygonal edge of two adjacent faces 810 connecting to theturned down or reduced radius portions of a rolling pin cylinder 830.Once the five pentagonal secondary faces 810 are connected to theprimary face 811, they can be connected to each other. The tertiaryfaces can be similarly connected to the secondary faces, and then toeach other, and then to the mounting plate face 812, to complete thespace frame. In this design, a cylindrical pin 830 and the contactingoffset v-grooves 835 from the two adjacent edges 840 of the adjacentfaces 810 act or function as a kinematic element. Contact of thecylinder with the offset vees prevents or resists over-constraint andthe attached pairs of springs 825 prevent or resist under-constraint.Thus, this kinematic element using a cylindrical pin and a pair oroffset vees or vee groves is an example of a different kinematic elementthan the kinematic elements 650A,B,C that were discussed previously.

Although the space frame 800 of FIG. 14A provides kinematic assemblyelements with spring loaded connections, it also includes redundantconstraints of the cylinder and vee connections along common edges 840.As a result, the rigidity of the system is significantly increased, andthe assembly method is common for every edge 840, simplifying overallmanufacture. But intermediate designs to that of FIG. 14A, using acombination of the kinematic elements with the cylindrical pins 830 andthe kinematic elements 650 (e.g., 650A, 650B, or 650C), located on otheror different edges 840 of the polygonal faces 810 can also be used toprovide improved or different kinematics between two or more polygonalfaces 810. This system also creates a large interior hollow space. andcan readily enable complete or partial disassembly for field replacementof components. Again, this space frame construction is not limited tothe dodecahedral geometry, and it also can be constructed using acombination of discrete and solid continuous faces.

As an alternative for a lower cost version of the space frame 800 ofFIG. 14A, the individual rolling pin cylinders 830 can be replaced witha stiff wire that is wrapped around the edges 840 that form theperiphery of a polygonal face 810. In this example, alternating face 810would have these wires. While the space frame would then be cheaper tomanufacture, some mechanical precision would be sacrificed.

In accordance with FIG. 11 , an internal space frame 500 can be a solidstructure with machined, cast, or printed, continuous faces 510.Alternately, a kinematic space frame 600, as depicted in FIGS. 12A-G,can be provided using a set of discrete faces 610 and interfacingkinematic elements 650. Alternative kinematic or partially kinematicspace frames 700 can also be provided that have a combination ofdiscrete and solid or continuous faces, as depicted in FIGS. 13A,B,C.Another alternative example space frame 800, depicted in FIG. 14A, canalso have a partially kinematic structure. The comparative kinematicperformance of these example space frames varies because of the designchoices that are made in the design and selection of the kinematicelements used, the use of a full set of discrete polygonal space framefaces (e.g., FIG. 12A or FIG. 14A) versus using a construction with afew continuous polygonal faces (e.g., FIG. 13B) versus using aconstruction with one or more larger structures with several continuouspolygonal faces (e.g., the crown structures of FIGS. 13A,C). Thecomparative kinematic performance can also depend on other factors, suchas the materials the polygonal faces or kinematic elements arefabricated from (e.g., steel, aluminum, zinc, bronze, invar, or FRP). Anassembled space frame can be pre-tested for kinematic performance. Forexample, a high precision kinematic space frame can control the relativepositioning of one face to another to spatial tolerances of ±0.025 mm orless.

As depicted, the space frame 600 of FIGS. 12A and 12G are nominallyfully kinematic due to an appropriate selection of kinematic elements650A,B,C between the various faces 610. Notably, although the spaceframe 800 of FIG. 14A has cylinder pin (830) based kinematic elementslocated in all the seams between all the polygonal edges 840, this spaceframe 800 is over constrained or partially kinematic. However, thekinematics can be improved by replacing some of the cylinder pin (830)based kinematic elements with alternate kinematic elements, such asusing appropriate selections of the kinematic elements 650A,B,C (seeFIGS. 12B-D) amongst the different seams. With appropriate selections,this space frame 800 can become nearly or fully kinematic.

By comparison, the space frame 700 of FIG. 13B includes both seamsacross which adjacent faces 710 are continuous or solid and rigid, andmany other open seams where adjacent faces are connected by kinematicelements 650 (e.g., 650A, 650B, or 650C). This frame can be fullykinematic relative to the appropriate selection of kinematic elements tospan the open seams. However, it is also partially kinematic as theseams between the adjacent continuous faces are nominally rigid as thesefaces were fabricated (e.g., machined, cast, or printed) as a continuousmaterial (e.g., steel). The rigidity of these multi-face structures canbe enhanced by fabricating the faces with stiffening ridges.Alternately, the rigidity can be reduced by fabricating these continuousfaces from one or more compliant materials (e.g., a polymer or plastic).Likewise, the space frames 700 of FIGS. 13A and 13C, which includecrown-like portions, are only partially kinematic, but the open seamscan be kinematically bridged, to for example, provide a fully kinematiclower hemisphere (e.g., FIG. 13A).

Thus, a partially kinematic space frame can have kinematic elements inall the seams between adjacent faces, but not have an appropriateselection of kinematic elements across all the seams so as to provide afully kinematic structure. The resulting structure can be either over orunder constrained. A partially kinematic space frame can alternately oralso have some seams between adjacent faces that are rigid, as forexample, the faces were fabricated from a single continuous material. Inexamples of this disclosure, an element or body is “fully kinematic” ifit is exactly constrained with the six degrees of freedom (DOFs) beingdeliberately and properly removed, and there being no redundantconstraints nor under constraints (e.g., the element or body is notpartially constrained). For the space frames, this means that theindividual elements or bodies (e.g., the individual faces or structureswith multiple continuous faces) are exactly constrained in the seamsbetween these bodies, so as to act or behave in composites as a rigidstructure.

Any of these example kinematic space frames, or variants thereof, can beapplied to the purpose of enabling an improved panoramic multi-cameracapture device 300 that has enhanced kinematic performance to bothmaintain structural integrity during conditions of potential over orunder constraint (e.g., changes in loading forces, gravity, thermalconditions) and thus help keep the camera channels (320) properlyco-aligned. But in addition, applying any of these example space framesfor the purpose of supporting a camera channels 320 for an improvedpanoramic multi-camera capture device 300 can also involve providingkinematic interfaces between the space frame faces and the lens housingsor camera channels.

Also, in the design of the space frame, it is useful to define a primaryface. In turn, it can be useful to define a primary camera channel thatcorresponds to the primary face. In some designs the mounting andadjustments for secondary or tertiary camera channels can have adifferent design or configuration than those for a primary camerachannel.

FIGS. 15A-C show a preferred approach for mounting lens housings tofaces or facets of a space frame that uses kinematic ball and veecontacts or features. In this design, nominally all camera channels andtheir lens housings 905 are identically assembled to the polygonal spaceframe facets 910. For example, they can be attached with 4-40 boltspassing through Belleville washers and a facet 910 of the space frame900 to attach to a lens housing 905 although nesting forces (e.g., 20 N)can be provided by other means. The interaction of the balls 930 to thevees 940 provides kinematic positioning that limits constraint issues.In particular, each ball 930 would sit in a vee 940 which would removetwo degrees of freedom at each ball 930, one on each face of the vee940. As the ball and v-groove features are placed on the underside ofthe lens housing 905, rather than in the seams 902 between adjacentcamera channels, it is easier to limit the seam width (e.g., ≤1 mm).

FIG. 15D depicts a second example of mounting a camera channel 920 withlens housing 905 to a face 910 or facet of a space frame 900. In thisillustration, the example space frame portion can be a one-piece crownstructure as is depicted, but it can also be a structure with multiplekinematically attached pieces (e.g., FIG. 12A, FIG. 14A, or FIGS.13A,B). The camera channel 920 with lens housing 905 shows theprotruding shape of an outer compressor lens element 925. The faces 910of the space frame 900 include three channel vee slots or vees 940 whichare used to kinematically align the face to the lens housing 905. Thelens housing 905 also has three precision balls 940 that are used toprecisely align that assembly to the vees 940 of the adjacent face 910.Three fasteners (not shown), such as bolts or magnets, then provideholding forces to retain the lens housing 905 to the face 910 of thespace frame 900. As an alternative to the balls 930, three pins (notshown), which are attached on the lower sides of the lens channelhousing 905, can contact three corresponding vees in a facet 910 of thespaceframe. The pin locations on the lens housing are 120° apart. Eachpin is perpendicular to the lower edge of the lens channel on the facewhere it is placed. Nesting forces could be achieved by placingcantilevered beams directly over each pin. In order to remove anambiguity of exact location of the pin/vee contact, the vees can have aslight curvature to ensure a point contact. As compared to the balls andvees approach which create point contacts, the pins would provide linecontacts that can result in much lower mechanical stress. However, theprotruding pins occupy more space, which can be difficult to provide forthis application.

In either case, it is also desirable to minimize the range of the forcesat the six contacts of a camera channel. This is to ensure positivecontact forces on all interfaces without exceeding yield stress values.The design approaches of FIGS. 15A-C can have improved performancerelative to other approaches, as the mechanical contacts can be closerto the center of mass, thereby reducing the moment arm.

To ensure the constraint pattern designed between the lens housing 920and the spaceframe (e.g., 500, 600, 700, or 800) results in exactconstraint, the design was evaluated against Maxwell's criteria forexact constraint (Douglass L. Blanding, 1995). In this design example, alens housing contacts the associated spaceframe polygonal facet usingpins, 120° apart, that rest in v-grooves. The lens housing 905 can bebolted to the associated spaceframe polygonal facet, which preventsunder constraint between the two.

Over constraint between a lens housing and the associated polygonalfacet can also be examined using Maxwell's criteria. These criteria aredesigned for four constraints as Maxwell does not discuss cases for fiveor six constraints, but nonetheless can be used to evaluateover-constraint by considering three initial constraints, and ensuringeach of the remaining constraints, when added, do not violate Maxwell'scriteria. Since all six constraints are sets of three coplanarconstraint pairs, no four lie in the same plane and thus the firstcriterion is satisfied. Furthermore, the maximum number of constraintsintersecting at an arbitrary point is two, and thus the second criterionis also satisfied. By inspection, it is clear that no two constraintsare parallel, and thus we pass Maxwell's third check. The finalcriterion states that a fourth constraint must not belong to the sameset of generators of a hyperboloid of one sheet as the initial threeconstraints. Identifying the initial three, skew, constraints as thoseprotruding from the same equivalent face of each vee, it is clear thateach of the remaining constraints is not a part of this set, as each ofthe remaining constraints intersects two of the original skew lines. Itmust, therefore, sit on the reciprocal generators of the hyperboloid,and thus Maxwell's fourth and final criterion is satisfied. One finalremaining check is to ensure that the constraint pattern is insensitiveto thermal expansion. To do so, it is observed that each constraintsurface is located radially from the origin, which is defined to be thecenter of the spaceframe face. Since all are located on a radial path,expansion will be the same proportional distance from the origin for allconstraints, meaning the center will not change and thus the kinematiccoupling is thermally stable.

FIG. 15B then depicts two adjacent lens channel housings 905 (lenselements not shown) mounted to two adjacent faces 910 of the spaceframe. To enable the intended optical performance, the width or gap ofthe mechanical seam 902 between adjacent camera channels 920 should besmall (e.g., <1 mm), while avoiding interference and being robustlymaintained during use. Small geometry changes at the spaceframe levelsuch as changing vee angle, vee dimensions, edge length, pin size, andball size all have a significant impact on seam width. FIG. 15C thendepicts a fully assembled space frame with an array of lens housings 905assembled to it, to enable an improved panoramic multi-camera capturedevice 300 (note: lens elements and other components are not shown).During device assembly, one or more of the lens housings 905, or othercomponents, such as the image sensors or datapath or power electronicsor cooling hardware will need to be attached. This can be done using avariety of features and tools, including tools with flexible cableextender.

As noted previously, the camera channels can be identically assembled tothe space frame using 4-40 bolts that pass-through Belleville washersand a facet of the space frame to attach to a lens housing. However, theorder of assembly can be important. For example, the tertiary camerachannels can be mounted first while accessing their 4-40 bolts via thesecondary channel faces. The secondary camera channels, adjacent to theprimary camera channel, can be added next, accessing their 4-40 boltsvia the top or primary face while using a flexible drive. The primary ortop channel can be added last, accessing its 4-40 bolts via the baseplate if the associated mount point can be removed.

It is noted that the balls, vees, and pins should all be surfacehardened so as to avoid structural failure. It may be advantageous toconduct a surface hardening process on the steel used to construct thefaces of the spaceframe, but due to strict tolerancing requirements andhigh cost of hardening small, localized areas, it can be more beneficialto design a recess in the faces of the spaceframe, and then attachpre-hardened vees. Such vees are readily available from suppliers suchas Bal-tec and could easily be incorporated into a space frame design.In several of the illustrated embodiments, springs are shown to couplethe faces of the space frame together, although other holdingmechanisms, including magnets, can be used. In particular, magnets maybe used to help hold a space frame together, and/or to hold the lens ahousing to a space frame face. As an example, permanent rare earthmagnets, part number D32SH from K&J Magnetics of Pipersville, PA, thatare 3/16″ dia.×⅛″ thick, with a pull force or 1-2 lbs., can be used.With an approximate gap between two facing magnets of 0.75 mm, theattracting strength between two magnets can be ˜0.5 lbs.

Also, as shown in FIG. 15D, during device assembly, the lens housing 905will fit into opening 915 with a mounting surface 935 being positionedin close proximity to the outer surface 912 of the face 910, where theprecise mounting is determined by the interaction of balls 930 with vees940. Balls 930 and vees 940 are located at nominally 120 degree spacing.As shown, mounting surface 935 is about midway up the length of the lenshousing 905. However, alternately a mounting surface 935 can be providedeither closer to the position of the image plane or the image sensor, orcloser to the position of the outer compressor lens element 925. Aspreferred approaches, the mounting surface 935 can be located near thecenter of mass or the center of gravity of the camera channel.

As is also shown in FIG. 15D, the lens housing 905 of camera channel 920can include magnets 945, balls 950, and flats 955 on the sidewalls ofthe lens housings. These features can provide kinematic constraintsbetween adjacent camera channels. In particular, the magnets can be usedto assist the kinematic mounting and alignment of a first camera channelto a second adjacent camera channel by providing a loading force. Theuse of such sidewall magnets (or latches or other mechanisms) can havegreater value if the mounting surface 935 is closer to the image planeor is closer to the outer compressor lens, rather than being proximateto the middle of the lens housing (as shown in FIG. 15D) or to thecenter of mass of the camera channel. In such cases where the mountingpoints are at or near an extreme mechanical position relative to thelength of a camera channel or objective lens assembly, sidewallkinematic features can help prevent a moment arm type rotation or pivotrelative to an applied force (including gravity).

In an alternate design where a space frame (900) supports the camerachannels from mounting points near the outer polygonal edges of theouter compressor lens elements 925, the width of material between theouter edges of opening 915 and an adjacent edge 917 can impact the widthof seams 902 between adjacent camera channels 920. In such cases, wherea space frame is provided proximate to the outer compressor lenselement, or the compressor lens group, compensating optical andmechanical design changes can be advantageous to reduce the impact onseam width. For example, the outer compressor lens element 925 and thelens housing 905 can be designed to hide the space frame 900 so it doesnot protrude through the seams and into the outer environment.Optically, this can mean that the outer compressor lens element 925bends incident light so steeply away from the polygonal lens edges thatmore space is created for an underlying space frame. As another optionto provide room for the space frame, superior design control to limitFront Color (FIG. 5E) to ≤0.5 mm and particularly to ≤0.1 mm can behelpful.

Also, as was suggested in FIG. 2B (see edges 132), the cut or cuts ofthe polygonal beveled edges 927, or the design of the lens housing 905and an associated lens holding plate 907 can be modified to provide moreroom for a space frame (900). Additionally, or alternately, the widthbetween the aforementioned edges (opening 915 to edges 917) of the spaceframe faces can be thinned so as to reduce an impact on the width ofseams 902 between adjacent camera channels.

The design of the faces 910 can be less flat, and more 3-dimensional, toprovide useful features and improved structural integrity.

As another option, the camera channels can be designed to haveadditional extended FOV 215 (FIG. 7 ) so as to optically hide anexpanded seam width (902). Depending on the amount of an extended FOV215 that is added to hide expanded seams 902 and a space frame 900, theoptical correction of residual parallax or perspective errors in thelens design can be compromised. Preferably these errors remainsub-pixel, but for some applications, a few pixels of error may be anacceptable trade-off for having a space frame positioned near the outercircumference of the improved multi-camera panoramic capture device(300).

Pre-assembled camera channels can be tested against an alignment fixtureto help ensure control over size, shape, and datum features, andadjustments can be made as appropriate. Then when an improvedmulti-camera panoramic capture device 300 is assembled, the individualcamera channels can be held or retained against the associated face ofthe polygonal space frame using one or more bolts, magnets, or latches,or adhesive(s), or combinations thereof. But in some instances, readyreplacement of components or a camera channel, for example, in theinstance of a failed sensor, broken lens element, or the like, may benecessary. Such a change can be done in a factory, but enabling fieldreplaceability is desirable. The space frame approach can enable thecamera channels to be field replaceable units (FRUs).

As one approach to remove one or more camera channels, the device can beaccessed via a polygonal facet through which any data and power cablingpasses through the space frame perimeter. If necessary, to access themounting features, this cabling can be removed. An appropriate tool canbe extended into the internal hollow central cavity of the space frameto the attachment points of a camera channel that needs to be removed,whether for replacement or repair, or to aid removal of another camerachannel. Given the polygonal geometry, a tool used for this purpose canhave a flexible shaft or extension so as to help access the mountingfeatures or mechanisms of the imaging channels that are angled away fromthe access port facet. Once released, a camera channel can then beextracted or removed by pulling it away from the device center. Datapathand power cabling can then be removed if that has not already occurred.A replacement pre-assembled camera channel can then be attached ormounted in place of one that was removed. If one or more materials oradhesives are being used to seal the seams or gaps between adjacentcamera channels, then they will also likely have to be replaced duringthis process.

In some examples, a support post or stalk would first be detached from aspace frame face that is the mounting interface. This allows access tothe base plate and the fasteners in the bottom of the primary assembly.Once the post is removed, the fasteners or bolts screws for the primarychannel can be accessible. Thereafter, the fasteners for the tertiarychannels may be the next most accessible. Lastly the screws to thesecondary assemblies are accessible. The space frame does not need to bedisassembled, and the lens housing assemblies have kinematic balls soreplacement with a new camera channels assembly would be possible toexacting tolerances. In some examples, the camera channels, includinglens housings and lens assemblies are nominally identical. Thus, onlyone part number is needed for assembly, storage and/or replacement.

It is noted that when replacing an image sensor assembly of a camerachannel, the corresponding circuit board may also need to be changed, asthey are typically matched sets. Also, in cases in which the device hasother than a dodecahedral geometry, and has more camera channels, thesize and number space frame faces and camera channels can complicate anassembly or repair activity. In particular, the available space toaccess components and the number of components, may be complicating.Alternately, or in addition, for some device designs, a retention orlocking mechanism, such as a latch, can be located within a seam betweenthe imaging channels. In this case, a tool can be inserted into a seamto release a retention mechanism.

In other instances, a face of a space frame may be damaged and need tobe replaced. It can be expected that the associated camera channel,whether damaged or not, would first be removed. However, it may benecessary to first remove multiple camera channels. The holdingmechanisms at the attached kinematic elements, whether springs, magnets,adhesives, or other mechanisms, would then be relaxed to release theface and to enable a replacement to be installed.

Although the illustrated space frame examples all show a dodecahedron,other overall shapes also are contemplated. For instance, the spaceframe may be constructed to form other three-dimensional shapes,including but not limited to other polyhedral shapes (including geodesicand Goldberg polyhedrons). Moreover, although the examples are generallydirected to structures providing 360-degree fields of view, in othersystems, a space frame may support different arrangements. For example,without limitation, a space frame can support multiple camera channelsin a hemispherical, quarter sphere, annular, or other shape.

In the prior examples, the lens housings and/or the space frame parts(e.g., the polygonal faces) can be formed using machined metals or castand machined metals like stainless steel. In other examples, othermaterials may be used. Some of these alternate materials includeplastics, including engineered or composite materials. For example,fiber-reinforced plastic (FRP) is a composite material made of a polymermatrix reinforced with fibers. The fibers are usually glass (infiberglass), carbon (in carbon fiber reinforced polymer), aramid, orbasalt. The polymer is usually an epoxy, vinyl ester, or polyesterthermosetting plastic. Composite plastics refers to those types ofplastics that result from bonding two or more homogeneous materials withdifferent material properties to derive a final product with certaindesired material and mechanical properties. Fiber-reinforced plasticsare a category of composite plastics that specifically use fibermaterials to mechanically enhance the strength and elasticity ofplastics. The glass fibers are extruded and drawn from materialsincluding SiO2, Al2O3, B2O3, CaO, or MgO, and then formed or woven intomats that are then imbedded in polymer during molding. Specifying theorientation of reinforcing fibers can increase the strength andresistance to deformation of the polymer. Glass reinforced polymers arestrongest and most resistive to deforming forces when the polymersfibers are parallel to the force being exerted, and are weakest when thefibers are perpendicular. In some cast resin components made of glassreinforced polymers, the orientation of fibers can be oriented intwo-dimensional and three-dimensional weaves. This means that whenforces are possibly perpendicular to one orientation, they are parallelto another orientation; this eliminates the potential for weak spots inthe polymer. Fiber-reinforced plastics are best suited for any designprogram that demands weight savings, precision engineering, definitetolerances, and the simplification of parts in both production andoperation. A molded polymer product is cheaper, faster, and easier tomanufacture than a cast aluminum or steel product, and can be machinedpost molding, while maintaining similar and sometimes better tolerancesand material strengths.

In some examples, a lens housing or a space frame facet can be moldedfrom a fiber-reinforced plastic. Although the CTE of glass fiberreinforced plastics varies with fiber direction, parallel orperpendicular (e.g., 15-55×10⁻⁶/° C.)., the values generally span therange between those of glass to those of optical plastics. A lenshousing molded with cross woven fibers can advantageously have a CTEthat is an average between that of optical glasses and plastics, therebyaiding thermal stability of the lens element positioning therein. Stillfurther examples may include fabricating die cast metal lens housings orpolygonal space frame facets using zinc-based alloys. Zinc die castingprovides thin walls and excellent surface smoothness. The zinc alloysadvantageously have a CTE relatively between that of most opticalglasses and most optical plastics, and thus it can readily enablethermal stability of an imaging lens assembly. Die cast zinc alloy partscan be machined post casting, but typically very little machining isrequired on precision zinc die castings because of the accuracy that canbe obtained, which is ˜5× better than that obtained with moldedfiberglass parts. Also, in other examples, materials may vary frompart-to-part. For example, some faces of a space frame can consist ofone type of material, while other faces consist of a second material.

In examples of this disclosure, a polygonal space frame has beendeveloped as an engineered kinematic structure to provide both precise,robust mounting support for an array of camera channels, to enableimproved multi-camera panoramic capture devices (300). The space frameprovides a useful hollow central volume that can be advantageously usedby imaging hardware (e,g., power and datapath cables) or as a passthrough for relayed image light. As another alternative, the supportedcameras 320 can act as objective lenses that provide light to fiberoptic relays rather than lens system based imaging relays (e.g., FIG. 9). In such a system, the fiber optic relays can be using optical fiberbundles that transfer image light from the respective image planesprovided by the objective lenses to a sensor. For image transfer,coherent optical fiber bundles can be used to relay the image light toan image sensor without free space optics. Each camera channel can havean associated image sensor, or several coherent fiber optic bundles canbe directed to a single image sensor.

This type of engineered kinematic space frame may have other opticalapplications or configurations. For example, it can be used to supportan array of cameras that look inwards into the hollow center, ratherthan outwards. It can also support other optical devices, such as lightsources, lasers, or sensors, that are directed either inwards oroutwards. As another example, a kinematic space frame can support anarray of light projection channels instead of camera channels. As anenablement, the image sensors can be replaced by addressable lightsource array devices that have light emitting pixels. For example, thesedevices can be micro-LED arrays, organic LED arrays (OLEDs), or laserarrays. Alternately, the image sensors can be replaced by opticalmodulator arrays (e.g., LCOS or DLP/DMDs) and illuminating light can beprovided by one or more separate light sources. Notably, these spaceframes can be used to enable improved multi-lens system devices, whetherfor image capture, image projection, or other optical purposes, in whichthe optical designs of the lens systems have not been optimized forparallax or perspective correction. This type of projection device canbe used in simulators, planetariums, or other domed theatres. Also inexamples, the space frame with mounted lenses may be contained inside aconcentric dome or a faceted dome. Without limitation, the dome mayprovide optical properties as well as a casing or covering for the lenselements mounted to the frame.

This type of engineered kinematic space frame may have other non-opticalapplications or configurations. For example, polygonal space frames havealso been used for interactive children's toys. However, space framesare more commonly used in architectural engineering to build latticework roofing supports or geodesic domes. Typically, a geodesic dome is ahemispherical or spherical thin-shell structure (lattice-shell) thathave a polyhedral shape based on a geodesic polyhedron. Engineeringemphasis is often directed at node structures that mount at the trussjoints. Domes can have a steel framework with the struts havingflattened ends and a single bolt secures a vertex of struts. Domes canalso be constructed with a lightweight aluminum framework which caneither be bolted or welded together or can be connected with a moreflexible nodal point/hub connection. The triangular elements of the domeare structurally rigid and distribute the structural stress throughoutthe structure, making geodesic domes able to withstand very heavy loadsfor their size.

Geodesic domes can have a system of cables that help hold the structuretogether. As such, they are referred to as tensile integrity ortensegrity structures, and they are comprised of elements that are undersimple tension or compression. Although a subset of these structures mayrepresent or appear as exactly constrained structures, in actuality theymay not be statically determinate structures. Whereas exactlyconstrained structures are always statically determinate. Additionally,tensegrity structures may not necessarily be precision structures thatcan maintain tight tolerances such as those that are required for mostoptical applications.

The engineered kinematic space frames of the present invention may havenon-optical applications that include architectural applications. Forexample, although many skyscrapers are designed to be earthquakeresistant, including by providing a compliant frame or foundation, abuilding designed and assembled using the types of kinematic spaceframes of the present invention may have improved resistance toearthquakes, wind, or other directional forces. As an architecturalstructure, a space frame may robustly and precisely hold a piece ofequipment in a pre-determined position. Alternately, the presentapproaches for engineered kinematic space frames may enable robust, easyto assemble, emergency shelters (e.g., similar to, but different thanthe structures by Shigeru Ban). A roof or covering can be provided overthe outside of the space frame.

What is claimed is:
 1. An imaging device comprising: a frame comprising:a first polygonal face having a plurality of first edges defining afirst periphery, a second polygonal face having a plurality of secondedges defining a second periphery, and one or more kinematic elementscoupling a first edge of the plurality of first edges to a first edge ofthe plurality of second edges; a first camera coupled to the firstpolygonal face and having a first lens, the first lens having aplurality of first lens sides defining a first lens periphery; and asecond camera coupled to the second polygonal face and having a secondlens, the second lens having a plurality of second lens sides defining asecond lens periphery, a first lens side of the first lens sidescontacting a second lens side of the second lens sides.
 2. The imagingdevice of claim 1, the frame further comprising: a third polygonal facehaving a plurality of third edges defining a third periphery; andadditional kinematic elements coupling a first edge of the plurality ofthird edges to a second edge of the plurality of first edges andcoupling a second edge of the plurality of third edges to a second edgeof the plurality of second edges, the imaging device further comprising:a third camera coupled to the third polygonal face.
 3. The imagingdevice of claim 2, the frame further comprising: additional polygonalfaces coupled to at least one of the first polygonal face, the secondpolygonal face, or the third polygonal face, to form a kinematic spaceframe, the imaging device further comprising: additional cameras coupledto the additional polygonal faces, the first camera, the second camera,the third camera, and the additional cameras configured to providesubstantially adjacent fields of view.
 4. The imaging device of claim 1,wherein the one or more kinematic elements comprise a first kinematicelement and a second kinematic element, wherein the first kinematicelement couples the second polygonal face to the first polygonal faceabout three degrees of freedom and the second kinematic element fixesthe second polygonal face to the first polygonal face about two degreesof freedom.
 5. The imaging device of claim 1, wherein the one or morekinematic elements comprise a cylindrical pin having a longitudinal axisextending generally parallel to the first edge of the plurality of firstedges and the first edge of the plurality of second edges, an outersurface of the cylindrical pin contacting a first datum surface on thefirst edge and a second datum surface on the second edge; a first springcoupled to the first polygonal face and to the cylindrical pin; and asecond spring coupled to the second polygonal face and to thecylindrical pin.
 6. The imaging device of claim 1, wherein the firstperiphery nominally matches the first lens periphery and the secondperiphery nominally matches the second lens periphery.
 7. The imagingdevice of claim 1, wherein a kinematic element of the one or morekinematic elements comprises a first portion secured to one of the firstpolygonal face or the second polygonal face and a second portion securedto the other of the first polygonal face or the second polygonal face,the first portion comprising a ball and the second portion comprising atleast one of a flat, a vee-groove, or a trihedral socket contacted bythe ball.
 8. The imaging device of claim 1, wherein the one or morekinematic elements comprise a cylindrical pin and offset vees.
 9. Theimaging device of claim 1, further comprising magnets or springsassociated with the one or more kinematic elements to provide holdingforces.
 10. The imaging device of claim 1, further comprising a balldisposed along a first edge of the first lens periphery and at least oneof a flat or a vee disposed along a second edge of the second lensperiphery, the ball contacting the at least one of the flat or the veeto maintain a seam between the first lens and the second lens.
 11. Theimaging device of claim 1, wherein at least one of the first camera iscoupled to the first face or the second camera is coupled to the secondface using at least one of magnets, vee groves, flats, and alignmentballs.
 12. The imaging device of claim 1, wherein the first camera ispositioned relative to the second camera such that a first low-parallaxvolume associated with the first camera at least partially overlaps asecond low-parallax volume associated with the second camera.
 13. Theimaging device of claim 1, wherein the frame defines a hollow center.14. The imaging device of claim 13, further comprising: a relay opticalsystem extending at least partially into the hollow center and throughan opening in a face of the frame opposite the first face.
 15. A framefor an imaging device comprising: a first polygonal face having aplurality of first edges defining a first periphery, a second polygonalface having a plurality of second edges defining a second periphery, andone or more kinematic elements coupling a first edge of the plurality offirst edges to a first edge of the plurality of second edges.
 16. Thefame of claim 15, wherein a kinematic element of the one or morekinematic elements comprises a cylindrical pin having a longitudinalaxis extending generally parallel to the first edge and the second edge,an outer surface of the cylindrical pin contacting a first datum surfaceon the first edge of the plurality of first edges and contacting asecond datum surface on the first edge of the plurality of second edges;a first spring coupled to the first polygonal face and to thecylindrical pin; and a second spring coupled to the second polygonalface and to the cylindrical pin.
 17. The frame of claim 15, furthercomprising: a third polygonal face having a plurality of third edgesdefining a third periphery; and additional kinematic elements coupling afirst edge of the plurality of third edges to a second edge of theplurality of first edges and coupling a second edge of the plurality ofthird edges to a second edge of the plurality of second edges.
 18. Theframe of claim 17, further comprising: additional polygonal facescoupled to at least one of the first polygonal face, the secondpolygonal face, or the third polygonal face, to form a rigid kinematicspace frame.
 19. The frame of claim 15, wherein the one or morekinematic elements comprise a first kinematic element and a secondkinematic element, wherein the first kinematic element couples thesecond polygonal face to the first polygonal face about three degrees offreedom and the second kinematic element fixes the second polygonal faceto the first polygonal face about two degrees of freedom.
 20. The frameof claim 15, further comprising one or more magnets or springsassociated with the one or more kinematic elements to provide holdingforces.